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THE    SIGNS    OF    LIFE 

FROM   THEIR  ELECTRICAL  ASPECT 


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LECTURES.  ON    PHYSIOLOGY,    PUBLISHED    UNDER    THE 
AUTHORITY    OF  THE    UNIVERSITY   OF    LONDON 


VOL.  L— EIGHT    LECTURES 

ON 

THE  SIGNS  OF  LIFE 

FEOM  THEIE  ELECTEICAL  ASPECT 


By  AUGUSTUS  D.  WALLER,  M.D,  F.R.S. 


NEW   YORK 
E.   P.   BUTTON   &   CO. 

1903 


Printed  in  Great  Britain 


PREFACE 

The  following  monograph  embodies  the  first  of  a  series  of 
lectures  on  Physiology,  delivered  by  the  Physiologists  of 
London  in  the  Laboratory  of  their  University. 

The  general  object  of  the  scheme  of  which  these  particular 
lectures  form  part,  is  to  present  the  results  of  recent  investiga- 
tion by  the  investigators  themselves — orally  and  with  experi- 
mental demonstration  in  the  lecture-room — outside  the  lecture- 
room  by  monographs  approved  by  the  University. 

With  the  modification  considered  suitable  for  the  case  of 
University  publications,  the  procedure  of  the  Royal  Society  as 
regards  the  printing  of  papers  in  the  Philosophical  Transactions 
has  been  adopted  by  the  Senate  of  the  University  of  London, 
the  regulations  in  connection  with  the  official  publication  of 
lectures  being  as  follows  : — 

"  Manuscripts  of  Lectures  delivered,  or  of  the  results  of  investiga- 
"  tions  made  in  the  Physiological  Laboratory  of  the  University,  shall, 
"  in  first  instance,  be  submitted  for  consideration  to  the  Physiology 
"  Committee,  to  be  referred,  if  considered  suitable,  to  two  referees,  who 
"  shall  be  requested  to  report  to  the  Physiology  Committee  as  to  their 
"  fitness  for  publication. 

"  Manuscripts  shall  be  accepted  only  if  reported  suitable  for  publi- 
"  cation — 

"  A.  By  reason  of  additions  to  knowledge  in  Physiology  and 
"  Experimental  Psychology, 

"  B.  By  reason  of  excellence  of  exposition  of  recent  additions  to 
"  knowledge  and  doctrine  in  Physiology  and  Experimental 
"  Psychology." 

The  present  eight  lectures  embody  in  large  measure  the 
recently  published  (and  unpublished)  results  of  my  own  current 


vi  PREFACE 

work  during  the  last  five  years.  They  are  in  continuation  of  a 
First  Series  of  Lectures  on  "  Animal  Electricity,"  published  in 
1897.  They  will  no  doubt  be  found  to  suffer  from  many  of  the 
disadvantages  inherent  to  the  nascent  state,  I  hope  that  they 
may  prove  to  possess  also  some  of  its  advantages. 

A.  D.  W. 

October  1903. 


CONTENTS 


LECTURE  I 

Aim  and  Purpose  of  the  Lectures — The  Subject-matter  of  Physiology 
— The  Signs  of  Life  ;  The  Sign  of  a  Sign  is  a  Sign  of  the  Thing 
itself — Two  Familiar  Instances  ;  on  Muscle  and  on  Nerve — A 
Proof  of  Chemical  Change  in  Seeds — An  Experiment  on  Muscle 
^Retinal  Currents — Vegetable  Currents — ^Terminology — Solu- 
tion-pressure— Summary       ...... 


LECTURE  II 

The  Prospect  —  Demonstration  of  Retinal  Currents  —  The  Initial 
Current — The  Principal  Fact ;  Subordinate  Features  —  Three 
Types  of  Response — Two  Opposed  Processes — Effects  of  Com- 
plementary Colours — Cause  :  Effect — Antesthetics — Retino-motor 
Effects  ........       21 


LECTURE  III 

Plan  of  this  Lecture — Electrical  Excitation  of  a  Frog's  Eyeball- 
Modification  of  the  Response  to  Light  subsequent  to  Tetanisa- 
tion,  and  during  Tetanisation — Effects  and  After-effects  of  Single 
Shocks  — "  Blaze-currents  " —  Polarisation  Currents  —  Electrocu- 
tion— Three  Types  of  Blaze-currents — The  Effect  is  greater  than 
its  Cause — Influence  of  a  Galvanic  Current — Some  Questions — 
The  Crystalline  Lens  .  .  .  .  .  -41 

LECTURE  IV 

Skin-currents  (of  the  Frog) — The  Normal  Current  is  "  Ingoing" — The 
Response  to  Indirect  Excitation  is  Outgoing,  Mixed,  or  Ingoing 
— The  Latent  Period  is  Two  Seconds  —  Fatigue  —  Atropine  — 
Mercuric  Chloride — The  Response  to  Direct  Excitation  is  Out- 
going— Summation — Effects  of  Tetanisation — Localisation  of  the 
Response  by  the  ABC  Method — Terminology      .  .  -59 


CONTENTS 


LECTURE  V 

TAGI 

The  Discharge  of  an  Electrical  Organ  in  Response  to  Direct  Excita- 
tion— Du  Bois-Reymond's  Summary — Similarity  between  "  Blaze- 
currents  "  of  the  Skin  and  "  Discharges  "  of  an  Electrical  Organ — 
Normal  Direction  of  the  Organ-current — A  Speculation  and  some 
Experiments  —  Further  Investigation  of  these  Currents  by  the 
ABC  Method — The  Positive  Polarisation  of  du  Bois-Reymond 
—  The  Polar  After-currents  of  Hering  and  of  Biedermann  — 
Ritter's  Tetanus  and  the  Post-anodic  Action  Current      .  .       76 


LECTURE  VI 

A  Representative  Experiment  —  Effects  of  Indirect  Excitation — 
Effects  of  Direct  Excitation  immediately  after  Death,  and 
Later — How  Long,  after  a  Cat's  Death,  can  a  Cat's  Foot  con- 
tinue to  Exhibit  Signs  of  Life  ? — More  A  B  C — A  Vegetable 
Surface  —  Surface  against  Surface  —  Anodic  and  Kathodic  — 
Biedermann  and  the  Frog's  Tongue — A  Warning  .  .       97 


LECTURE  VII 

Observations  on  the  Human  Skin — Du  Bois-Reymond's  Experi- 
ments— Tarchanofif's  Observations — Sweat-prints — Introduction 
of  Ions  through  the  Skin     .  .  .  .  .  .114 


LECTURE  VIII 

The  Fallacy  of  the  Electrodes — Water  Transport  at  Anode  or  Kathode 

— Alteration  of  Resistance  at  Anode  or  Kathode    .  .  .129 


APPENDIX 

The  Normal  Circuit — Galvanometer,  Coil,  Compensator,  Electrodes, 
and  Keyboard — Photographic  Recording — Lippmann's  Capillary 
Electrometer — Special  Keys — Units  of  Resistance  and  of  Con- 
ductance        .  .  .  .  .  .  .  •     ^S^ 


Index       ,......••    i73 


THE    SIGNS    OF    LIFE 


"  The  greatest  thing  a  human  soul  does 
in  this  world  is  to  see  something,  and  tell 
what  it  saw." — RUSKIN, 


LECTURE  I 

Aim  and  Purpose  of  the  Lectures — The  Subject-matter  of  Physiology — The 
Signs  of  Life  ;  The  Sign  of  a  Sign  is  a  Sign  of  the  Thing  itself — Two 
Familiar  Instances  ;  on  Muscle  and  on  Nerve — A  Proof  of  Chemical 
Change  in  Seeds — An  Experiment  on  Muscle — Retinal  Currents — 
Vegetable  Currents  —Terminology — Solution-pressure — Summary. 

§  I.  Aim. — The  aim  and  purpose  of  these  lectures  is 
extremely  simple.  By  the  liberality  of  the  Senate  of  the 
University,  seconded  by.the  liberality  of  one  of  its  distinguished 
graduates,  the  teachers  and  students  of  physiology  separately 
working  in  the  many  scattered  Colleges  of  the  Metropolis,  are 
enabled  to  bring  to  its  University,  as  to  a  focus,  the  best  they 
have  to  bring. 

I  shall  not  take  upon  myself  to  utter  any  forecast  of  the  fate 
of  this  effort  towards  concentration,  nor  attempt  to  justify  our 
undertaking  by  any  high-flown  anticipations.  All  that  I  venture 
to  say — on  behalf  of  my  colleagues  as  well  as  on  my  own  behalf 
— is  that  we  believe  that  in  Physiology  as  in  other  subjects,  there 
exist  in  this  great  metropolis,  scattered — I  had  almost  said  lost 
— in  the  several  colleges  that  now  form  part  of  the  University, 
the  elements  which  collectively  constitute  a  university  school  of 
learning. 

And  if  I  might  venture  to  characterize  by  one  word  what 
to  my  mind  is  the  most  essential  mark  of  a  teacher  of  university 
rank,  I   should    say  that  it  is  that  such  teacher  should  be  an 

A 


2  THE  SIGNS  OF  LIFE  [lect. 

active   student — not    merely   a    learn^^    man,   but   a    leammg- 


man. 


And  that  leads  me  to  what  we  hope  is  to  be  the  keynote 
and  dominant  tone  of  these  lectures  —  namely,  that  they  are 
especially  to  belong  to  what  may  be  termed  the  growing  surface 
of  our  knowledge.  Each  one  of  us  is  to  bring  here  the  know- 
ledge that  he  has  himself  gathered  at  first  hand  in  the  particular 
garden  that  he  has  chosen  to  work  in,  and  of  such  knowledge  it 
is  an  infallible  characteristic  that  it  is  unsatisfied,  incomplete — 
an  ever  green  surface,  a  surface  of  encroachment. 

And  so  this,  our  talking-room,  rests  upon  a  foundation  of 
working-rooms,  and  these  in  turn  ultimately  rest  upon  our 
working-rooms  scattered  throughout  the  colleges  of  the  University 
of  London,  at  University  College,  at  King's  College,  at  the 
London  medical  colleges,  and  at  the  colleges  for  women. 

Another  point :  A  critic,  a  friendly  critic,  in  the  days  when 
these  lectures  were  first  talked  of,  wanted  to  know  to  whom  they 
were  to  be  given,  urged  indeed  that  in  this  great  scattered 
University  of  London  there  are  not  a  dozen  students  requiring 
or  caring  for  advanced  lectures  in  physiology  ;  he  said  that  we 
should  have  to  lecture  to  each  other.  I  hope  we  shall  lecture  to 
each  other  and  be  each  other's  pupils.  Looking  to  this  list,  I 
think  I  may  say  that  during  the  last  twenty  years  I  have  been 
the  pupil  of  every  one  of  my  present  colleagues,  and  I  hope  I 
have  not  finished  learning  from  them  ;  and  I  am  very  sure  that 
if  this  laboratory  fulfils  its  true  function,  we,  the  professed 
teachers,  will  receive  as  well  as  give  instruction  from  and  to  the 
students  and  frequenters  of  the  laboratory. 

§  2.  Sudject.— The  subject-matter  of  physiology  is  Life— or 
more  properly  speaking— living  things,  vegetable  as  well  as 
animal.  And  although  physiologists,  in  common  with  all  man- 
kind, must  at  times  indulge  themselves  in  speculations  concerning 
the  origin  of  life,  the  existence  of  vital  force,  the  immortality  of 
protoplasm  and  other  insoluble  philosophical  problems,  their  real 
daily  work  is  the  hardly  less  extensive  task  of  learning  how 
plants  and  animals  live,  in  what  particulars  their  living  organs 
and  tissues  differ  from  the  same  organs  and  tissues  when  they 


1.]  .  NOTA  NOTM  3 

have  ceased  to  live,  how  quickly  they  live,  how  much  they  live, 
upon  what  they  live,  and  how  while  they  live,  they  absorb, 
transform,  distribute,  and  dispense  the  energy  stored  in  food 
and  manifested  in  each  act  of  life.  In  one  word  our  task  as 
physiologists  is  to  study  the  signs  of  life.  To  say  that  these 
are  lectures  on  the  signs  of  Life  is  to  say  that  they  arejectures 
on  Physiology. 

The  Signs  of  Life. 

The  signs  by  which  we  can  always  recognise  that  living 
matter  is  living  are : — 

1.  Its  reducing  or  deoxygenating  power ; 

2.  Its  exhalation  of  carbon  dioxide  ; 

3.  Its  excitability  ;  and 

4.  The  electrical  signs  of  its  chemical  activity. 

The  present  series  of  lectures  will  be  in  chief  measure  drawn 
from  the  fourth  head — and  I  should  have  taken  for  their  title 
the  electrical  signs  of  life,  were  it  not  that  the  electrical  signs  by 
themselves  should  not  in  my  opinion  be  divorced  from  other 
signs ;  and  are  indeed,  when  so  divorced,  of  comparatively  small 
general  importance — matter  of  special  and  technical  interest 
rather  than  a  chapter  in  General  Physiology. 

The  point  of  view  to  be  taken  can  be  formally  presented 
in  terms  of  the  classical  axiom  of  the  logicians — nota  notce  est 
nota  rei  ipsius — inasmuch  as  chemical  change  being  a  sign  of 
life,  and  electrical  change  a  sign  of  chemical  change,  it  follows 
that  electrical  change  is  a  sign  of  life — meaning  by  "  sign " 
an  universal  attribute  of  our  subject  rather  than  an  occa- 
sional or  exceptional  incident — a  ^^ propritirn "  rather  than  an 
*'  accidens." 

From  which  formal  position  we  may  proceed  a  step  further, 
and  recognise  that  in  the  study  of  electrical  change  we  have  the 
most  delicate  and  one  of  the  most  convenient  means  of  approach 
towards  an  answer  to  these  two  questions  addressed  to  matter 
that  may  be  living  or  not-living  : — 

1.  Are  you  alive? 

And  when  this  first  qualitative  question  has  been  answered  :— 

2.  How  much  are  you  alive  ? 


4  THE  SIGNS  OF  LIFE  [lect. 

§  3.  Instances. — The  two  instances  of  electrical  effects  with 
which  you  are  no  doubt  familiar  already,  are  : — 

I.  The  negative  variation  of  muscle ;  2.  The  negative 
variation  of  nerve :  and  I  shall  presently  use  the  first  of  these 
phenomena  to  illustrate  the  parallelism  between  the  mechanical 
sign  of  life  (contraction)  and  the  electrical  sign  of  life  (negative 
variation). 

Turning  now  to  the  syllabus  of  this  first  lecture,  you  find 
there  several  headings  that  are  more  or  less  familiar  to  you,  that 
I  shall  nevertheless  recall  to  your  attention,  for  the  sake  of  the 
point  of  view  I  ask  you  to  take. 

Omitting  any  attempt  to  define  "  Life  and  the  Living  State," 
we  shall  in  first  resort  seek  to  recognise  what  are  the  principal 
differences  between  matter  that  is  alive  and  matter  that  is  not- 
alive.  And  take  note  in  passing  that  by  this  division  into  alive 
and  not-alive,  or  living  and  not-living,  we  include  dead  matter 
as  a  sub-division  of  not-living  matter,  which  we  consider  as  falling 
into  the  complementary  sub-classes  of  matter  that  has  previously 
lived  (but  is  now  "  dead  ")  and  matter  that  has  not  previously 
lived  (and  is  called  "  inert "). 

And  although  our  physiological  problems  are  in  most  cases 
concerned  with  the  comparisons  and  distinctions  that  we  are 
able  to  institute  between  living  and  dead  matter,  we  shall  find — 
for  the  sake  of  logical  discourse  in  dealing  with  matter  in  a  state 
of  what  has  been  called  latent  life  or  suspended  animation — that 
it  is  convenient  to  make  a  first  division  into  living  and  not-living, 
and  a  sub-division  into  dead  and  inert  in  accordance  Avith  this 
dichotomous  scheme : — 

Matter. 


Living.  Nol-living;. 


Formerly  Not  formerly 

living.  living  =  Inert. 


Capable  of  living  Not  capable 

again  =  Dormant,  of  living 

e.g..,  a  dry  seed.  again  =;  Dead. 

This  scheme  has  been  drawn  up  with  the  particular  purpose 
of  showing  how,  in  my  opinion,  we  should  logically  deal  with,  e.g.^ 


I.]  .    ARE  SEEDS  LIVING  OR  DEAD?  5 

the  vexed  question  whether  a  seed  (or  a  dry  rotifer,  or  a  hen's 
egg,  or  a  tissue  completely  "  anaesthetised  ")  is  alive  or  dead. 

We  shall  have  to  recognise  that  the  one  general  and  all- 
embracing  sign  of  life,  whether  we  consider  a  complete  organism, 
or  a  single  organ,  or  an  isolated  part  of  an  organ,  is  Movement — 
movement  of  the  whole  mass,  or  that  movement  of  its  molecules 
which  we  characterise  as  physical  and  chemical  and  physico- 
chemical.  All  living  matter  is  the  seat  of  chemical  change,  or  if 
you  prefer  it,  physical  or  physico-chemical  change. 

Now  dry  seeds,  kept  for  long  periods  in  hermetically  closed 
vessels,  have  not  been  found  to  manifest  any  evidence  of  the 
most  fundamental  and  general  chemical  change  occurring  in 
living  matter,  viz.,  a  production  of  CO2.  Their  chemical  reply 
to  the  question,  "  Are  you  alive  ?  "  has  been  "  No." 

But  does  this  negative  answer  "  not-alive "  imply  that  such 
seeds  are  dead  ?  Evidently  not,  as  may  be  seen  if  under  suitable 
conditions  of  temperature,  moisture,  and  so  forth,  they  are  found 
to  germinate  and  grow  into  plants.  So  that  a  seed,  in  so  far  as 
it  does  not  manifest  chemical  change,  is  not  proved  to  be  living ; 
and,  inasmuch  as  it  germinates,  is  proved  not  to  be  dead. 
Evidently,  here  is  a  dilemma ;  in  the  absence  of  an  objective 
chemical  sign  of  life,  we  have  no  right  to  say  that  a  seed  is  alive  ; 
it  is,  as  far  as  we  can  tell,  not-alive ;  in  the  presence  of  its 
subsequent  germination  we  are  assured  that  it  is  living,  and  that 
therefore  it  was  not  dead.  And  the  usual  manner  of  escape 
from  this  dilemma  of  the  seed  which  is  neither  living  nor  dead, 
is  to  say  that  it  is  in  a  state  of  latent  life,  during  which  there  is 
a  complete  suspension  of  chemical  changes  characteristic  of  the 
living  state. 

I  will  not,  at  this  early  stage,  stop  to  comment  upon  the 
contradiction  involved  in  this  form  of  words,  nor  upon  the  fact 
that  it  involves  contradiction  of  the  fundamental  axiom  that  the 
essential  attribute  and  objective  sign  of  the  living  state  is 
chemical  movement.  But  I  will  offer  for  your  consideration  a 
different  mode  of  escape  from  the  dilemma. 

It  is  possible — or  rather  certain — firstly,  that  our  means  of 
chemical  investigation  are  not  refined  enough  to  reveal  to  us 
the  smallest  and  most  infinitesimal  changes  that  may  be  going 


6  THE  SIGNS  OF  LIFE  [lect. 

on  in  an  apparently  dry  and  perfectly  dormant  seed ;  and 
secondly,  it  is  possible  that  chemical  change  may  be  completely 
and  absolutely  arrested  {e.g.,  by  low  temperature)  without  that 
arrest  being  of  necessity  final  and  definitive. 

I  will  place  evidence  before  you  of  this  first  point,  which  I 
have  investigated  at  some  length.  As  to  the  second,  which  I 
have  not  myself  investigated,  I  will  only  mention  that  it  appears 
to  be  established  by  the  observations  of  Horace  Brown,*  who 
found  that  dry  seeds  kept  for  no  hours  in  closed  vessels  at  a 
temperature  of  —  183°  to  —  192°,  i.e.,  seeds  in  which  the  arrest  of 
chemical  change  must  be  considered  to  have  been  absolutely 
complete,  germinated  quite  normally  when  they  were  placed 
under  suitable  conditions  of  temperature  and  moisture. 

The  inadequacy  of  our  chemical  methods  to  reveal  small  or 
infinitesimal  chemical  changes  taking  place  in  seeds  is,  I  think, 
proved  in  two  ways.  We  know,  in  the  first  place,  that  kept 
seeds  wear  out,  that  the  percentage  of  seeds  that  germinate  and 
grow  is  smaller  and  smaller  with  the  number  of  years  they  have 
been  kept.  The  deterioration  is  more  or  less  rapid  according 
to  the  nature  of  the  seed  and  the  character  of  its  protective 
coats,  but  in  every  known  instance  there  is  deterioration  sooner 
or  later,  and  I  think  you  must  admit  such  deterioration  to  be 
sign  and  proof  that  chemical  change  has  taken  place. j- 

§  4.  Seeds. — A  still  closer  and  more  manageable  proof  that 
seeds  may  be  the  seat  of  chemical  changes  which  chemical 
methods  are  inadequate  to  reveal,  is,  as  I  shall  develop  in  a 
future  lecture,  afforded  by  an  electrical  method.  As  formally 
laid  down  above,  electrical  changes  are  the  token  of  chemical 
changes,  which  are  the  token  of  the  living  state.  And  these 
electrical   changes   are    manifested    by  seeds   long   before   the 

*  Proc.  Roy.  Soc,  vol.  Ixii.,  p.  160,  1897. — Thiselton-Dyer  has  gone 
further,  viz.,  to  -  250°  to  —  252°,  Proc.  Roy.  Soc,  vol.  Ixv.,  p.  361. 

+  The  continued  formation  of  aleurone  granules  in  very  old  seeds  is  in 
certain  instances  an  objective  sign  of  the  occurrence  of  slow  chemical 
change.  The  germination  of  "mummy  wheat"  must  be  set  down  as 
apocryphal,  in  spite  of  the  wheat  sheaf  shown  in  a  Paris  museum  grown 
from  Mariotte's  mummy  wheat.  The  wheat  was  given  to  Mariotte  by 
Arabs. 


I.]  .HOW  MUCH  ARE  YOU  ALIVE?  7 

manifestation  of  any  microscopical  or  chemical  signs  that  they 
are  the  seat  of  a  physiological  activity.  And  yet  we  have  not 
reached  a  limit ;  although  our  electrical  test  is  more  delicate 
and  closer-searching  than  either  a  morphological  or  a  chemical 
test,  we  may  not  flatter  ourselves  that  it  makes  sensible  to  us 
the  real  ultimate  (or  initial)  chemical  movements  of  infinitesimal 
magnitude  that  herald  (or  attend  upon)  the  awakening  of  the 
dormant  embryo — the  birth  of  a  renewed  life. 

And  so,  if  driven  to  the  foot  of  the  wall  by  the  question,  "  Is' 
this  good  seed  living  or  dead  ?  "  I  should  answer,  "  I  can't  tell  by 
looking  at  it,  nor  by  chemically  testing  it,  but  come  back  in  an 
hour,  and  I  will  show  you  that  this  seed,  since  you  say  it  is  a 
good  seed,  is  an  actually  living  seed ;  and  then,  if  you  like,  I 
will  kill  it  and  show  you  how  differently  it  behaves.  At  this 
moment  I  do  not  know  whether  or  no  infinitesimal  chemical 
change  is  going  on  in  the  seed,  but  I  believe  that  such  infini- 
tesimal change  (if  it  exists)  may  be  suppressed  (by  low  tempera- 
ture) without  thereby  making  the  seed  dead" 

Hence,  in  verbal  physiological  specification  of  a  good  seed,  I 
should  say,  in  order  of  logical  subordination  :  Matter — Not-living 
— Formerly  living — Capable  of  living  again. 

This  has  been  a  dialectical  parenthesis.  Before  leaving  the 
topic  let  me,  however,  utilise  it  in  illustration  of  the  answers 
desired  (and  in  some  cases  obtained)  to  these  two  chief 
questions  : — Are  you  alive  ?     How  much  are  you  alive  ? 

To  the  qualitative  question,  "  Are  yau  alive  ? "  the  seed 
response  is  "  Yes,"  "  No,"  or  "  Doubtful " — "  Yes  "  being  an 
electrical  response  of  considerable  magnitude,  "  Doubtful "  or 
•'  No  "  being  little  or  no  response. 

To  the  quantitative  question,  "  How  much  are  you  alive  ? " 
the  affirmative  response  comes  in  the  forms  of  units,  which  are 
fractions  of  a  volt,  as  in  this  instance,  where  seeds  (Phaseolus) 
of  different  years  are  submitted  to  the  quantitative  question. 

It  is  of  course  impossible  for  me  to  carry  out  a  long  series 
of  trials  like  this  on  the  lecture  table  ;  it  will  be  sufficient  for  the 
purpose  of  illustration  if  I  show  you  three  trials — one  on  an 
assuredly  living  seed,  one  on  an  assuredly  dead  seed  (that  has 
been  killed  by  heat),  and  a  third  on  a  very  old  seed  of  which  I 


THE  SIGNS  OF  LIFE 


[lect. 


do  not  know  beforehand  whether  it  is  aHve  or  dead  (but  which 
I  believe  to  be  dead  as  it  dates  from  the  year  i860).  And  at 
the  end  of  this  lecture,  if  you  care  to  see  the 
trial,  I  will  test  some  very  old  seeds  indeed,  that 
were  given  to  me  by  Mr  Percy  Newberry,  who 
combines  the  qualifications  of  botanist  with  those 
of  Egyptologist.  They  are  seeds  collected  by 
himself,  and  placed  by  him  as  dating  from  the 
twelfth  dynasty,  i.e.,  as  being  something  like  4400 
years  old.  I  need  hardly  say  that  no  such  un- 
doubtedly old  seeds  will  give  any  electrical 
response,  nor  will  they  germi- 
nate. I  have  previously  made 
both  tests. 


Voib 


•oiao 


■0/00 


•003O 


\Experiinenti\ 


Year. 


The  first  seed  gives,  as  you 
see,  a  large  electromotive  re- 
sponse. The  other  seeds  give 
no  response  at  all.  The  first 
seed  is  alive,  the  others  are 
dead.  We  shall  return  to  these 
I  wish  in  this  first  lecture  to 
exhibit  to  you  two  other  experimental  illustrations  as  typical 
of  the  kind  of  problem  and  argument  with  which  we  have  to 
deal. 


Fig.  I. — Average  electrical  response  of 
seeds  of  five  successive  years.  The 
ordinates  represent  the  average  vol- 
tage of  response,  which,  as  stated  in 
the  text,  is  taken  as  the  index  of 
vitality.* 

matters    in    a    future    lecture ; 


I  5.  Muscle. — Muscle  is  a  favourite  object  of  physiological 
experiment ;  it  gives  sign  of  life  by  contracting  when  it  is 
stimulated — either  directly,  by  stimulation  of  the  muscle  itself, 
or  indirectly,  by  stimulation  of  the  nerve  that  is  its  motor  nerve. 
And,  roughly  considered,  its  mechanical  response  or  contraction 
is  measure  of  the  degree  of  vitality  that  it  possesses.  No  one 
doubts  that  the  contraction  of  a  muscle  is  sign  and  proof  of  its 
state  of  life,  and  that  the  degree  of  contraction  and  the  work  of 
which  that  contraction  is  capable,  are  ccBteris  parihis  measure 

*  Proc.  Roy.  Soc,  vol.  Ixviii.,  p.  87. 


•] 


MUSCLE  CURRENTS 


of  the  amount  of  vitality  possessed  by  muscle.  A  weak  muscle 
can  do  less  work  than  a  strong  muscle,  and  a  given  muscle  in 
the  course  of  fatigue,  or  of  that  last  act  of  life  that  we  call 
death,  can  give  less  and  less  extensive  contraction,  and  effect 
a  smaller  and  smaller  amount  of  work.  Pari passic  with  declin- 
ing contraction  we  witness  declining  electromotive  response,  and 
we  admit  or  assume  that  the  common  substratum  of  the  decline, 
whether  mechanical  or  electrical,  is  decline  of  chemical  activity. 
An  excised  muscle  has  been  set  up  to  show  this  parallelism 
between  mechanical  and  electrical  response.  A  lever  attached 
to  the  tendon  indicates  to  you,  by  its  excursion  on  a  smoked 
glass  plate,  the  extent  or  height  of  the  mechanical  movements 
(contraction).       A   galvanometer    connected    to  the   muscle   by 


MechdnicaL  Response. 


ELectnc<3.L  Response. 


Fig.  2. — Simultaneous  records  of  a  series  of  muscular  contractions,  and  of  the 
corresponding  series  of  negative  variations.  The  method  and  apparatus  for  obtaining 
such  records  is  described  in  the  Appendix,  p.  l6o,  Fig.  63. 

wires  and  unpolarisable  electrodes,  indicates  to  you,  by  the 
excursion  of  the  reflected  spot  of  light,  the  extent  or  voltage  of 
the  accompanying  electrical  movements.  The  muscle  is  excited 
indirectly,  by  excitation  of  its  nerve,  and,  as  you  see,  the  two 
sets  of  movements,  mechanical  and  electrical,  run  an  approxi- 
mately parallel  course — both  are  large  together  or  small  to- 
gether, and  if  one  is  absent,  so  is  the  other.  You  would  notice, 
however,  on  closer  comparison,  that  the  parallelism  is  not  perfect, 
the  mechanical  and  electrical  responses  are  not  an  exact  replica 
of  each  other,  and  the  defect  of  correspondence  is  particularly 
apparent  in  simultaneous  records  of  the  two  sets  of  responses. 

I  cannot  at  present  enter  further  upon  this  difference,  I  think 
it  requires  further  study ;  if  you  ask  which  of  the  two  records  is 
the  more  faithful  indicator   of  the  chemical  changes  of  which 


10  THE  SIGNS  OF  LIFE  [lect. 

they  are  both  the  tokens,  I  shall  answer  that  in  my  opinion  the 
electrical  indications  are  the  more  faithful ;  they  are  without 
doubt  the  more  sensitive  since  they  are  still  of  quite  consider- 
able magnitude  when  a  muscle  is  so  weak  as  to  scarcely  con- 
tract at  all,  nor  be  competent  to  raise  a  lever  to  any  measurable 
height.  In  the  pair  of  records  you  have  just  seen,  the  electrical 
indications  are  reduced  to  manageable  size  by  shunting  the 
galvanometer. 

§  6.  Retinal  currents. — The  third  object  of  experiment  is  a 
frog's  eyeball  set  up  in  a  dark  chamber  between  unpolarisable 
electrodes  which  are  connected  with  a  galvanometer.  By  open- 
ing a  shutter  the  eyeball  is  illuminated  at  any  desired  time  for 
any  desired  period.  When  I  do  this,  there  is  no  mechanical 
movement  of  the  eyeball,  at  least  no  coarse  mechanical  move- 
ment,* but  you  witness  a  large  and  obvious  electrical  change. 
Holmgren,  who  first  discovered  this  effect,  found  by  a  series  of 
experiments  in  which  he  made  separate  trial  of  the  several 
parts  of  the  eyeball,  that  the  electrical  effect  was  of  retinal 
origin.  Light  acting  upon  the  retina  excites  it ;  in  ourselves 
the  subjective  token  of  that  excitation  is  a  sensation  ;  in  the 
isolated  eyeball  the  objective  token  of  excitation  is  an  electri- 
cal change.  The  detailed  description  of  these  changes  will 
form  the  subject  of  my  next  lecture,  but  I  should  be  glad  if 
you  would  take  note  of  what  you  have  actually  witnessed  in 
the  present  case.  The  eyeball  has  been  set  up  on  electrodes, 
so  that  its  fundus  rests  upon  one  electrode,  while  its  cornea  is 
touched  by  the  other  electrode,  the  spot  of  light  was  deflected 
to  the  left  during  the  illumination,  and  returned  to  its  original 
position  after  illumination.  I  touch  one  terminal  of  the  gal- 
vanometer with  a  bit  of  zinc,  and  the  other  terminal  with  a 
finger  of  the  other  hand ;  the  spot  moves  to  the  left,  the  ter- 
minal I  touched  with  the  bit  of  zinc  is  that  to  which  the 
corneal  electrode  is  connected :  from  which  I  conclude  that 
the  current  during  illumination  was  from  cornea  to  fundus.  I 
choose   to  call   this  direction   "  negative,"  and  shall   denote   as 

*  On  closer  examination,  there  may  be  detected — (i)  contraction  of  the 
pupil,  (2)  protrusion  of  pigment,  (3)  retraction  of  cones. 


I.]  .  RETINAL  CURRENTS  11 

"positive"  the  opposite  direction  from  fundus  to  cornea.  And 
I  recognise  in  the  deflection  to  the  left  that  we  have  just 
witnessed  what  I  am  accustomed  to  regard  as  a 
reaction  of  the  third  stage,  viz.,  a  negative  current, 
directed  from  before  backwards  in  the  eyeball.  And 
I  may  just  mention  that  a  few  hours  ago,  when  I 
put  up  this  eyeball  for  ex- 
periment (under  difficulties 
inseparable  from  the  pres- 
ence of  belated  workmen    in 

a  new   laboratory),  it  gave  a  ,,         , 

in.-  u  T  NormaL    response. 

positive  deflection,  such  as   1  '^ 

have  learned  to  be  typical  of 

a  fresh  and  normal   eyeball,  and   have   chosen  to  characterise 

as  a  reaction  of  the  first  stage. 

These  have  been  details  of  the  laboratory,  details  that  you 
have  hardly  followed  as  I  had  to  do,  to  make  plain  to  myself 
(and  state  to  you)  what  was  the  direction  of  current  in  the 
eyeball  indicated  by  the  direction  of  movement  of  the  spot  of 
light.  Those  of  you  who  are  actual  workers  will  appreciate 
the  importance  of  attention  to  such  details,  and  the  hopeless 
confusion  arising  from  doubtful  determinations  of  direction  of 
observed  currents.  Those  of  you  who  content  themselves  with 
the  literature  of  the  subject,  will  find  it  almost  impossible  to 
realise  what  writers  mean  by  "positive"  and  "negative"  effects. 

But  the  response  we  have  just  seen  is  not  of  the  type  that 
I  wish  to  show  in  a  first  lecture ;  it  is  of  what  will  be 
described  later  as  a  response  of  the  third  type,  negative  instead 
of  positive ;  the  eyeball  may  have  been  kept  waiting  too  long, 
or  have  been  accidentally  compressed  in  the  course  of  pre- 
paration. So  I  shall  repeat  the  experiment  on  another  eye- 
ball that  has  just  been  carefully  prepared  and  set  up  for  me 
by  the  assistant. 

\Experiinent.^ 

And  now,  as  you  see,  the  response  to  light  is  a  normal 
response  of  the  first  type,  viz.,  positive,  for  the  spot  has  moved 
to  your  right  during  the  illumination,  indicating  current  through 


12  THE  SIGNS  OF  LIFE  [lect. 

the  eyeball  from  fundus  to  cornea — and  I  make  sure  of  this 
direction  once  more  by  touching  the  fundus  electrode  with  a 
bit  of  zinc,  and  seeing  that  the  spot  moves  to  your  right. 

Let  me  make  one  more  pair  of  trials  to  assure  you  that 
it  has  been  luminous  radiation  in  particular,  and  not  thermal 
radiation,  that  has  excited  the  retina  of  this  eyeball.  I  repeat 
the  exposure  just  as  before,  with  the  standard  candle  at  un- 
altered distance  (5  feet),  but  with  an  alum  cell  interposed  to 
filter  off  most  of  the  heat,  and,  as  you  see,  the  response  is  no 
smaller  than  before.  Finally,  I  take  away  the  alum  cell,  and 
expose  the  retina  to  the  very  sensible  heat  of  a  black  hot 
surface  of  metal,  and,  as  you  see,  there  is  no  response  at  all 
to  heat  without  light. 

§  7.  The  nicclianical  excitability  of  vegetable  protoplasm. — The 
fourth  and  last  experiment  that  I  wish  to  show  is  a  very  simple 
one,  but  in  my  judgment  a  fundamental  experiment  in  general 
physiology.  It  relates  to  the  mechanical  excitability  of  vegetable 
protoplasm,  and  is  calculated  to  convince  you  of  the  essential 
identity  between  the  excitatory  responses  of  vegetable  and  of 
animal  protoplasm.  Those  of  you  who  are  students  of  physi- 
ology or  of  physiological  botany,  are  no  doubt  acquainted  with 
various  instances  of  movements  in  plants  consequent  upon 
mechanical  excitation  ;  and  you  probably  know  from  the  observa- 
tion by  Burdon-Sanderson  on  Dionaea,  that  these  movements 
are  accompanied  by  electrical  effects.  You  may  take  it  that  the 
excited  plant-stuff  is  the  seat  of  chemical  change,  that  this 
change  is  of  the  nature  of  a  disintegration  from  large  complex 
molecules  to  smaller,  simpler  molecules,  that  this  disintegration 
has  involved  an  increased  osmotic  pressure,  whence  turgor  of 
certain  cells,  whence  movement  of  petioles  and  leaves.  And 
with  these  chemical  changes  there  are  of  course  associated 
electrical  changes. 

But  these  notions  are  to  be  extended,  and  we  are  to  recognise 
further  that  any  and  every  living  vegetable  protoplasm,  when 
excited,  undergoes  chemical,  and  therefore  electrical,  change, 
whether  it  actually  moves  or  not. 

I  have  used  all  kinds  of  vegetable  protoplasm,  usually  during 


•] 


PLANT  CURRENTS 


13 


the  months  of  March  and  May,  and  for  the  experiment  now  on 
the  table  my  favourite  object  has  been  the  vigorously  growing 
shoots  of  a  vine.  But  in  this  bleak  month  of  May  (1902)  the 
vine  shoots  have  not  yet  appeared,  and  I  have  therefore  taken 
a  less  favourable  object,  viz.,  the  petioles  of  ivy-leaves,  which,  in 
comparison  with  young  vine  shoots,  must  be  looked  upon  as 
rather  a  sluggish  variety  of  vegetable  tissue.  So  I  shall  take  a 
stronger  mechanical  stimulus  than  usual. 

The  petiole  of  an  ivy-leaf  is  fastened  by  modelling  wax  to  a 
glass  plate ;  to  two  points,  5  cm.  distant  from  each  other,  un- 
polarisable  electrodes  are  connected,  and  attached,  of  course,  by 


Fig.  4. — "Plant-guillotine"  for  the  demonstration  of  the  mechanical 
excitability  of  vegetable  protoplasm.  The  shutter,  visible  only  on  one  side 
B,  by  which  the  twig  or  shoot  is  excited,  is  represented  as  having  dropped. 


wires  to  the  galvanometer.  Two  slips  of  wood  (weighing  5 
grams  each)  running  in  vertical  grooves,  are  suspended  by  catches 
I  cm.  above  the  petiole  close  to  the  electrodes,  which  we  will 
call  A  and  B.  I  let  go  the  slip  B,  which  strikes  the  petiole  near 
the  B  end  with  an  energy  of  5  c.g.m.m.,  the  spot  flies  off  scale  to 
your  right.  (I  readjust  the  spot,  and  when  it  is  steady,  let  go 
the  slip  A,  and  now  the  spot  flies  off  to  your  left.)  I  test  for 
direction  as  described  above,  by  touching  the  galvanometer 
terminals  with  a  bit  of  zinc  wire,  and  seeing  that  by  touching  B 
the  spot  goes  to  right  (and  by  touching  A  it  goes  to  left).  I 
know  that  when  the  petiole  was  excited  at  B  there  was  current 


14  THE  SIGNS  OF  LIFE  [lect. 

through  it  from  B  to  A  (while  when  it  was  excited  near  A  there 
was  current  in  it  from  A  to  B). 

Is  there  any  doubt  in  your  mind  whether  these  have  been 
physiological  responses,  for  which  the  essential  condition  is  that 
the  ivy  petiole  should  be  alive  ?  There  should  be  such  a  doubt 
in  your  mind,  and  you  should  set  the  doubt  at  rest  by  repeating, 
or  making  me  repeat,  the  experiment  on  a  petiole  of  which  the 
molecular  mobility  has  been  abolished,  i.e.,  on  a  petiole  that  has 
been  killed  or  otherwise  immobilised.  I  might  kill  it  at  once  by 
plunging  it  into  hot  water,  but  to  do  this  I  should  have  to 
remove  it  from  the  electrodes  and  replace  it,  which  takes  time ; 
and  even  at  best,  when  the  petiole  has  been  replaced  as  carefully 
as  possible  as  it  was,  you  cannot  be  quite  sure  that  I  have 
exactly  replaced  the  petiole.  So  I  shall  otherwise  immobilise 
it,  in  a  way  that  will  allow  me  to  leave  petiole  and  electrodes  in 
statu  quo,  viz.,  by  sending  through  it  currents  of  such  strength 
that  the  living  stuff  will  be  completely  stunned :  which  I  now 
do,  and  then  repeat  both  trials  as  before,  exciting  at  A  and  then 
at  B,  without,  as  you  see,  any  response  in  either  case.  The 
previous  effects  you  witnessed  were  therefore  physiological. 

I  8.  "  ZincativeT — So  far  so  good,  there  is  no  doubt  what- 
ever about  the  facts,  the  excitatory  currents  are  precisely  such 
as  are  aroused  by  excitation  of  animal  protoplasm.  But  how 
are  we  to  label  them  ? 

Following  the  best  authorities — Faraday,  Maxwell,  du  Bois- 
Reymond — we  should  say,  referring  to  the  pole  under  our 
observation,  that  B,  the  excited  spot,  is  negative  to  A,  the  non- 
excited  spot  (or  A,  the  excited  spot,  negative  to  B,  the  non- 
excited  spot ;  but  since  this  confirmatory  experiment  is  confusing 
we  will  henceforth  omit  it,  and  consider  only  B  excited,  and  A 
non-excited). 

And  as  a  matter  of  fact,  this  has  been  the  terminology 
followed  by  physiological  writers. 

But  in  course  of  time,  and  especially  in  consequence  of  the 
polemic  that  took  place  between  du  Bois-Reymond  and 
Hermann,  the  meaning  of  the  term  "  negative  "  underwent  a 
curious   twist.     Du    Bois-Reymond    found    that    the    "  resting 


PLANT  CURRENTS 


15 


Fig.  5.- 


-Vine-shoot.     Electrical  Effects  of  Mechanical  Excitation 
(10  centigrammetres)  before  and  after  boiling. 


The  first  four  excitations  (before  boiling)  give  responses  of  0.060,  0.045,  0.045,  and 
0.040  volt.     The  5th,  6th,  and  7th  excitations  (after  boiling)  give  no  response. 

The  deflection  preceding  the  ist  excitation  is  by  0.04  volt,  and  the  resistance  of  the 
stem  between  leading-off  electrodes  was  500,000  ohms.  The  deflection  preceding 
the  5th  excitation  is  by  o.oi  volt,  and  the  resistance  of  the  boiled  stem  was 
6o,coo  ohms. 


Vobb 

•04 


5  m. 


Fig.  6. — Experiment  (3023). — Bean-Radicle  (Phaseolus)  3  inches 
lono-  and  quite  etiolated,  incubated  in  the  dark  at  25°  for  five  days.  Led 
off  to  recording  galvanometer  by  two  unpolarisable  electrodes,  A  and 
B.  The  radicle  is  struck  transversely  near  A^  then  near  B^  by  a  bristle 
fixed  to  the  end  of  a  revolving  rod.  In  each  case  the  deflection  is  such 
as  to  indicate  that  the  struck  spot  is  rendered  electropositive  (galvano- 
metrically  negative)  to  the  unstruck  spot.  The  effects  are  completely 
abolished  by  strong  tetanisation. 


16  THE  SIGNS  OF  LIFE  [lect. 

current "  of  quiescent  muscle  and  of  nerve  is  diminished  when 
the  muscle  contracts  or  when  the  nerve  is  excited  ;  he  called  this 
diminution  "a  negative  variation  of  the  previous  current  of 
rest."  Hermann  then  showed  that  this  negative  variation  of  a 
current  of  rest  (or  current  of  injury)  is  only  a  special  case  of  a 
more  general  phenomenon,  and  that  active  tissue  is,  properly 
speaking,  negative  to  resting  tissue,  quite  irrespective  of  any 
previous  "  pre-existing  "  current.  And  from  the  fact  that  active 
tissue  is  negative,  and  that  the  action  is  propagated  in  muscle 
and  in  nerve,  physiologists  adopted  the  expression  "  negativity 
of  action,"  and  spoke  of  propagation  of  a  wave  of  negativity  in 
the  excitable  tissue.  And  little  by  little  a  confusion  of  thought 
established  itself;  the  origin  of  the  expression  "  negativity"  was 
lost  sight  of,  active  tissue  was  spoken  of  as  being  "  electrically 
negative  "  and  then  "  electro-negative  " — which  is  clearly  wrong 
in  the  accepted  physical  sense  of  this  term.  In  physical 
language  the  neg-a^tve  po/e  of  a.  voltaic  couple  is  connected  with 
the  electro-positive  element,  the  positive  pole  with  the  electro- 
negative element.  And  when  a  writer  had  escaped  an  actual 
misnomer,  an  ambiguity  that  was  even  more  mischievous  to 
clear  thinking  became  effective ;  a  state  of  negativity  of  action, 
propagated  from  active  to  non-active  parts,  arouses  in  the 
reader's  mind  the  picture  of  a  current  directed  in  the  tissue 
when  connected  by  two  points,  active  and  non-active,  from  former 
to  latter,  i.e.,  from  "negative"  to  "positive."  Now  this  direction 
is  correct,  but  it  is  disturbing  to  one's  thought  to  regard  current 
as  directed  from  negative  to  positive.  And,  in  point  of  fact,  the 
language  is  actually  wrong ;  the  adjectives  "  positive "  and 
"  negative  "  as  used  by  Faraday  refer  to  the  poles,  current  is  of 
course  from  positive  to  negative  in  an  external  circuit,  positive 
and  negative  refer  to  an  external  circuit,  and  should  not  be  used 
with  reference  to  the  internal  circuit.  It  is  a  misuse  of  terms  to 
say  that  current  in  the  tissue  is  directed  from  negative  to  positive 
pole.  The  proper  thing  to  say  is  that  direction  in  the  tissue  is 
from  electro-positive  to  electro-negative,  that  active  tissue  is 
electro-positive  to  resting  tissue,  that  a  wave  of  electro-positivity 
travels  in  muscle  (or  in  nerve)  from  an  excited  spot. 

But,  in  the  present  state  of  our  physiological  literature,  is  it 


'^ZlNCAtiVfi'' 


If 


wise  to  attempt  to  use  the  proper  expressions  ?  No  doubt  the 
confusion  is  very  great,  no  doubt  the  main  bulk  of  our  electro- 
physiological literature  is  totally  unintelligible  to  physicists  and 
to  most  physiologists.  Shall  we  not,  however,  lay  the  foundation 
of  a  further  mass  of  worse-confounded  confusion  by  any  sudden 
and  unauthorised  endeavour  to  call  white  white  and  black  black, 
when  for  the  last  twenty  or  thirty  years  our  leaders  have  been 
content  to  call  white  black  and  black  white  ? 

I  hardly  like  to  hazard  an  opinion,  but  in  presence,  on  the 
one  hand,  of  the  impossibility  of  clear  thought  and  speech,  with 
external  adjectives  for  internal  relations,  and,  on  the  other  hand, 
the  mental  impossibility  of  obtaining  a  sudden  reversal  of 
language  which  is  endeared  to  physiologists  by  its  familiarity 
and  its  obscurity,  I  have  adopted  a  new  and  barbarous  word 
that  avoids  the  pole  name  "  negative "  and  the  element  name 
"  electro-positive,"  yet  implies  both  names.  And  for  the  present, 
at  any  rate,  awaiting  a  better  word,  or  a  clearer  understanding, 
I  shall,  whenever  occasion  seems  to  demand  the  word  to  make  a 
meaning  clear,  use  the  expression  sincaiive,  to  imply  "  electro- 


The  current  of  a  Daniel  cell  is 
from  copper  to  zinc  through  the 
galvanometer,  and  from  zinc  to 
copper  in  the  cell  itself. 


Fig.  7, 


A  nerve  current  is  from  unin- 
jured to  injured  spot  through  the 
galvanometer,  and  from  injured 
to  uninjured  spot  in  the  nerve 
itself.  The  injured  spot  is  "zinca- 
tive." 


motive  like  the  zinc  of  a  voltaic  couple " ;  zinc  is,  as  we  all 
know,  negative  as  to  its  external  relation  by  its  pole,  and  electro- 
positive as  to  its  internal  relation  in  the  cell.  Current  in  the 
cell  is  from  zinc  to  copper,  in  the  tissue  from  more  active  to  less 
active ;  an  active  tissue-element  is  electro-positive  to  a  resting 
tissue  element,  or  (under  protest)  an  active  tissue  element  is 

u 


U  THE  StGNS  OP  LIFE  [lect. 

negative  to  a  resting  tissue  element ;  but  whether  we    call    it 
electro-positive  or  negative,  the  active  element  is  "  zincative." 

§  9.  "  Solution-pressured — To  those  of  you  who  are  accus- 
tomed to  think  about  currents  through  electrolytes,  in  terms 
of  ions  creeping  through  a  solvent,  this  matter  should  present 
itself  in  a  very  simple  light.  Active  protoplasm  takes  on  a 
higher  "  solution-pressure "  (in  the  sense  with  which  Nernst 
has  made  us  familiar),  and  electro-positive  ions  migrate  in 
greater  abundance  from  protoplasm  to  lymph.  There  is  then 
"  current  of  action,"  and  I  do  not  think  that  we  need  at  this 
stage  pause  to  object  whether  this  increased  pressure  may 
be — not  of  the  protoplasm  itself — but  of  paraplasm  (?  fat, 
?  carbohydrate)  set  in  motion  by  protoplasm.  Whatever  the 
nature  of  the  ions  may  be,  we  must  picture  them  as  laden 
with  positive  charges,  and  pressing  into  the  lymph-bath  from 
spots  where  they  have  become  congregated  and  accumulated, 
i.e.,  in  and  around  the  meshwork  of  living  matter.  Imagine 
simple  hydrogen  kations,  or  if  you  like,  more  complex 
hydrogen  and  carbon  kations,  as  issuing  forth  from  a  solid 
coast  to  a  fluid  atmosphere,  where  their  oxidation  is  con- 
summated—  forming  water,  lactic  acid,  and  carbon  dioxide 
as  their  typical  end-products.  These  notions,  in  my  way  of 
thinking,  are  the  physiological  connotations  involved  in  the 
brief  statement  that  ^^  active  tissue  is  zincative!'  And  if  you 
have  gone  so  far,  you  will  almost  certainly  go  one  step 
further,  and  imagine  that  just  as  a  zinc  rod  that  has  given  off 
zinc  ions  to  its  surrounding  medium,  is  for  the  moment,  nega- 
tively charged,  so  a  core  or  stem  of  living  stuff,  immediately 
after  a  discharge  of  positively  charged  ions  is  relatively  negative. 
Current  of  action  is  thus  followed  by  an  opposite  after-current ; 
du  Bois'  "  negative  variation  "  is  followed  by  Hering's  "  positive 
after-variation."  But  I  do  not  wish  to  pursue  this  point  in  detail 
now,  for  there  are  no  experiments  in  evidence  before  you.  An 
opportunity  of  demonstration  may  perhaps  arise  at  a  future 
lecture. 

I    10.  Summary. — Will  you   think   of  these  things?     I  will 


I.]  .  SUMMARY  19 

try  to  place  myself  in  the  position  of  a  listener,  and  offer  some 
criticism  of  what  you  have  just  listened  to. 

You  would  find,  if  you  critically  compared  the  lecture  with 
its  syllabus,  that  many  points  mentioned  in  the  syllabus  have  not 
been  fairly  met  by  the  lecture,  that  the  order  of  the  spoken  (and 
written)  description  differs  from  the  order  of  items  promised  by 
the  syllabus,  that  points  have  been  talked  about  of  which  there  is 
no  mention  in  the  syllabus.  To  which  my  defence  is,  that 
memoranda  of  a  printed  paper  cannot  be  placed  in  the  same 
logical  order  as  the  thoughts  and  comments  that  arise  from 
experiments  in  the  act  of  demonstration.  And  so  I  have  left 
untouched  (for  the  present)  the  headings  "  an  excised  nerve," 
"a  piece  of  skin,"  "  a  green  leaf,"  "  a  cut  flower,"  "  a  stem,"  in 
the  hope  that  you  may  for  yourselves  realise  how  these  things 
associate  themselves  in  the  mind  of  any  one  planning  a  group  of 
considerations.  The  reason  of  such  association  may  perhaps  be 
made  plain  in  the  course  of  these  lectures. 

You  may  have  found  it  rather  perplexing  to  be  told  at  some 
length  that  positive  means  negative,  and  that  negative  means 
positive.  Some  of  you  have  hitherto  been  quite  satisfied  to 
talk  about  the  negative  variation  of  contracting  muscle  or  of 
excited  nerve.  I  believe  that  these  expressions  are  nearly 
always  empty  to  utterers  and  hearers  alike,  and  I  have  deliber- 
ately tried  to  disturb  your  easy  acceptance  and  use  of  paper 
language,  and  put  you  to  the  trouble  of  mentally  imaging  the 
facts  denoted  by  the  words.  The  points  to  be  definitely 
registered  from  what  you  have  witnessed,  are: — 

(i)  From  the  muscle  experiment:  that  pari  passu  with  its 
contraction^  its  ordinary  and  indubitable  sign  of  life,  an  electrical 
change  is  proof  and  measure  of  its  state  of  life. 

(2)  From  the  eyeball  experiment :  that  we  have  witnessed 
an  electrical  response  to  luminous  stimulation. 

(3)  From  the  ivy  leaf:  that  vegetable  as  well  as  animal  proto- 
plasm, while  alive,  gives  an  electrical  response  to  mechanical 
excitation. 

(4)  From  the  seed  experiments  :  that  the  electrical  response 
to  electrical  excitation  can  be  utilised  as  a  measure  of  "  vitality." 


20  THE  SIGNS  OF  LIFE  [lect.  i. 


REFERENCES 

Burdon-Sanderson. — "On  the  Electro-motive  Properties  of  the  Leaf  of 

Dionoea,"  Proc.  Roy.  Soc,  p.  495,   1873  ;  Phil.  Trans.  Roy.  Soc,  1882  ; 

Ph'l.  Trans.  Roy.  Soc,  p.  417,  1888. 
Horace  Brown  and  F.  Escombe. — "  Note  on  the  Influence  of  very  Low 

Temperatures  on  the  Germinative  Power  of  Seeds,"  Proc.  Roy.  Soc,  Ixii., 

1897,  p.  160. 
Thiselton-Dyer. — "  On  the  Influence  of  the  Temperature  of  Liquid  Hydro- 
gen oh  the  Germinative  Power  of  Seeds,"  Proc.  Roy.  Soc,  Ixv.,   1899,  p. 

361. 
Waller. — "  An  Attempt  to  estimate  the  Vitality  of  Seeds  by  an  Electrical 

Method,"  Proc  Roy.  Soc,  vol.  Ixviii.,  1901,  p.  79. 
Waller. —  Lectures  on  Animal  Electricity,  1897. 
Waller. — "  Researches  in  Vegetable  Electricity,"  International  Congress 

of  Physiologists,  Turin,  September  1901. 
Waller. — "  Electrical  Response  of  Vegetable  Protoplasm  to  Mechanical 

Excitation,"  Proc  Physiol.  Soc,  November  1901. 
Burch. — "On  the  Interpretation  of  Photographic  Records  of  the  Response 

of  Nerve  "  [Terminology],  Proc.  Roy.  Soc,  vol.  Ixx.,  1902,  p.  194. 

^ote. — The  misuse  of  the  terms  "  ELECTRO-POSITIVE  "  and  "  electro-NEGA- 
TIVE,"  to  which  I  called  attention  six  years  ago  in  the  first  paragraph  of  Lectures  on 
Animal  Electricity,  is  now  very  generally  recognised.  In  the  Oxford 'Laboratory 
the  remedy  proposed  is  to  simply  transpose  the  words  ;  but  until  a  general  agreement 
is  arrived  at  that  "POSITIVE"  (new  style)  is  to  be  the  equivalent  of  "NEGATIVE"  {o/d 
style),  and  vice  versa,  I  think  the  remedy  will  be  even  more  prejudicial  to  clear  think- 
ing than  the  disease.  I  do  not  think  the  word  "  zincative  "  has  yet  fully  served  its 
purpose,  and  shall  therefore  continue  to  use  it  when  it  appears  to  me  to  be  required. 


LECTURE    II 

The  Prospect — Demonstration  of  Retinal  Currents — The  Initial  Current — 
The  Principal  Fact ;  Subordinate  Features — Three  Types  of  Response 
— Two  Opposed  Processes — Effects  of  Complementary  Colours — 
Cause  :  Effect — Anaesthetics — Retino-motor  Effects. 

§  II.  Prospective. — It  is  my  intention — in  the  eight  days' 
laboratory  excursion  which  I  hope  some  at  least  of  my  present 
hearers  will  complete — to  visit  several  apparently  disconnected 
points  of  physiology.  And  while  I  shall  not  attempt  to  show 
you  at  once  that  these  points  are  in  fact  intimately  connected, 
I  will  name  them  to  you  now,  and  promise  that  their  uniting 
bonds  shall  become,  evident  to  you  in  due  season — by  your 
own  thinking,  rather  than  by  my  talking.  "  The  Excitability 
of  the  Retina  " — "  The  Excitability  of  Vegetable  Protoplasm  " 
— "Skin  Currents" — "The  Development  of  a  Hen's  Egg" — 
"  Secreto-motor  Action  " — "  The  Action  of  Anaesthetics."  These 
are  some  of  the  topics  that  are  at  present  linked  together  in  my 
mind,  as  on  a  thread  of  intention,  towards  the  next  few  lectures. 

And  before  I  commence  to  tell  the  first  bead  of  my  chaplet, 
let  me  make  further  confession  of  faith,  and  outline  to  you  the 
sort  of  purpose  and  intention  by  which  scientific  research  may 
be  animated.  There  are  two  chief  moments  in  the  life  of  every 
explorer — the  moment  of  discovery,  and  the  moment  of  dis- 
closure, when  the  first  pleasure  is  shared  with  others.  But  before 
this  second  moment  may  be  enjoyed,  a  language — not  necessarily 
of  words  alone — must  be  common  to  talker  and  to  hearer.  The 
talker  must  in  a  measure  generalise  his  language,  the  hearer 
must  in  a  measure  specialise  his  understanding,  and  learn  the 
meaning  of  terms  and  formulae  and  labour-saving  symbols  that 
are  current  coin  in  the  daily  dealings  of  every  specialist, 


22  THE  SIGNS  OF  LIFE  [lect. 

I  shall  do  my  best  to  talk  in  simple  language,  but  I  know 
that  we  shall  often  be  forced  to  fall  back  upon  technical  terms. 
The  ideal  way  would  be,  in  first  place,  to  have  written  a  mono- 
graph in  the  dry  and  freely  technical  language  of  a  Philoso- 
phical Transactio7is  paper ;  in  second  place,  to  retell  the  same 
story  here  in  the  simple  words  and  homely  metaphors  by  which 
we  ordinarily  attempt  to  tell  each  other  what  we  are  thinking 
about.  It  will  not  be  possible  to  me  to  strictly  follow  this  ideal 
way,  but  I  shall  do  my  best  to  justify  narrative  by  reference  to 
duly  accredited  publications  ;  and  as  to  technicalities,  well,  perhaps 
some  degree  of  physiological  technicality  may  be  excused  in  the 
Physiological  Laboratory  of  the  University  of  London. 

Every  one  here  is  no  doubt  acquainted  with  the  physiology 
of  vision,  in  so  far  as  it  is  given  in  the  text-books.  You  have 
studied  the  eyeball  as  an  optical  instrument,  containing  a  living 
sensitive  surface  that  receives  the  focussed  (or  unfocussed)  radi- 
ations of  light.  You  have  studied  the  course  and  the  central 
cortical  terminus  of  the  nerve  fibres  leading  from  retina  to 
brain.  You  know  that  the  thing  as  seen  by  you  is  your 
subjective  picture,  aroused  by  the  objective  retinal  pattern  of 
the  objective  field  of  vision.  You  have  proceeded  to  the  closer 
study  of  the  objective  retinal  change  from  which  the  subjective 
visual  sensation  takes  origin,  and  have  learned  that  the  objective 
effects  of  light  acting  upon  the  retina  of  an  excised  but  sur- 
viving eyeball  are  : — a  bleaching  of  its  visual  purple,  a  movement 
of  expansion  of  its  pigment  cells,  a  movement  of  contraction  of 
its  cones,  and,  as  in  every  case  of  physico-chemical  change,  an 
accompanying  electrical  change. 

One  more  preliminary  consideration.  Our  own  retina,  that 
arouses  in  our  own  brain  the  detailed  images  of  complicated 
objects  when  detailed  images  are  focussed  upon  it,  gives  rise 
to  diffuse  sensations  of  light  and  to  the  fantastic  appearances 
called  phosphenes  when  it  is  stirred  into  action  by  direct 
mechanical  or  electrical  stimuli.  Mechanical  pressure  of  the 
eyeball,  or  an  accidental  blow  upon  it,  or  an  electrical  current 
traversing  it,  anything,  in  short,  that  suddenly  disturbs  the  retina, 
elicits  in  consciousness  the  specific  subjective  symptoms  of  a 
suddenly   disturbed   retina,   formless   or    fantastic,   a   blaze    of 


11.] 


EYEBALL  CURRENTS 


23 


flashing  lights,  or  a  succession  of  colours,  in  accordance  with 
the  accidents  and  irregularities  of  such  coarse  artificial  disturb- 
ance. And  no  doubt — could  we  only  detect  it — the  physico- 
chemical  disturbance  is  attended  by  an  electrical  disturbance 
The  latter  will,  however,  be  most  easily  demonstrated  to  you 
with  an  excised  eyeball. 


12.  Demonstration. — Such   an   eyeball    has  been    removed 

71 


■  Inductonum^ ' 
Fig.  8. — Frog's  eyeball  between  unpolarisable  electrodes  for  demonstration  ot 
the  electrical  effects  of  light  and  of  electrical  excitation.  The  circuit  from  the  eye  is 
completed  through  a  compensator,  secondary  coil,  and  a  galvanometer.  The  arrows 
through  the  eyeball  and  the  galvanometer  indicate  the  direction  of  the  initial  current 
and  of  the  normal  response.  Arrows  near  the  compensator  wires  indicate  the  direction 
of  a  compensating  counter-current. 

as  carefully  as  possible  a  few  moments  ago  from  a  pithed  frog. 
"Carefully"  in  this  connection  means  with  as  little  compression 
of  the  eyeball  as  possible,  and  in  point  of  fact  such  compression 


24 


THE  SIGNS  OF  LIFE 


[lect. 


has  been  nearly  quite  avoided  by  cutting  the  frog's  head  in  half, 
taking  up  the  fragment  with  forceps,  and  trimming  away  the 
orbit  from  the  eyeball  with  scissors.  The  eyeball  is  now  resting 
upon  the  clay  pad  of  an  unpolarisable  electrode,  the  pointed  pad 
of  the  second  electrode  touches  the  cornea,  the  actual  contact 
being  by  a  droplet  of  salt  solution.  The  electrodes  are  con- 
nected to  a  galvanometer.  The  eyeball  and  electrodes  are 
enclosed  in  a  black  box  with  a  hole,  tube,  and  shutter  opposite 
the  eye,  so  that  when  desired  the  latter  can  be  exposed  for  any 
required  time  to  light  of  any  required  strength. 

The  connections  are  such  that  the  fundus  of  the  eyeball  is 
attached  to  the  south  terminal,  and  the  cornea  to  the  north 
terminal,  of  the  galvanometer  as  in  Fig.  3  or  in  Fig.  8,  with  the 
keyboard  unplugged.  (The  circuit  includes  a  compensator  and 
a  secondary  coil,  to  be  used  in  our  next  Lecture.) 

O-OIO  f 1 1 1 1 1 1 

§  13.  The  initial  cur- 
rent. —  Notice  as  a  first 
point  that  the  natural  cur- 
rent of  the  eyeball  has 
given  current  through  the 
galvanometer  from  N  to 
S  terminal,  i.e.,  that  within 
the  eyeball  it  has  been 
from  fundus  to  cornea. 
Notice  further  the  fact  that 
this  current  is  rapidly  de- 
clining. The  spot  deflec- 
,  ,   ,.  .  r     r     ,      ted  to  your  right  is  sink- 

— Normal  declimng  current  of  a  frogs      .  "^ 

The  rate  and  shape  of  decline  resemble      mg    tO    yOUr   left   towards 
those  of  a  blaze  current.  j^S     2erO     point*         If    WC 

could  afford  to  wait,  we  should  see  the  spot  reach  the  zero  and 
continue  its  journey  to  the  opposite  end  of  the  scale,  indicating 
to  us  that  the  eyeball  current,  at  first  directed  from  fundus  to 

*  The  lecture- room  is  east  and  west,  the  former  being  the  lecturer's  end. 
The  galvanometer  is  on  a  bracket  fixed  to  the  east  wall  of  the  room,  and  the 
movements  of  its  suspended  magnet  are  shown  by  a  vertical  spot  of  light 
reflected  to  a  transparent  scale  placed  on  the  lecture-table.     The  audience 


o-ooz 


0-006 

Fig.  9 
eyeball. 


GO  mm. 


0-0CI5Z 

0-0058 


ii.].'  ,  '^BLAZE-CURRENT"  25 

cornea  (positive),  is  ultimately  directed  from  cornea  to  fundus 
(negative).  We  shall  get  a  better  general  view  of  this  gradual 
change  by  plotting  a  curve  of  readings  taken  at  regular  intervals 
(Fig.  9).  I  think  you  will  agree  with  me  that  the  entire  curve, 
falling  with  diminishing  rapidity  towards  and  beyond  the  zero 
value,  is  badly  named  when  it  is  called  a  current  of  rest,  and 
that  it  cannot  possibly  be  only  a  subsiding  current  of  injury  at 
the  transverse  section  of  the  optic  nerve.  I  think  and  speak  of 
it  as  a  declining  manipulation  blaze  caused  by  the  unavoidable 
mechanical  disturbance  that  occurs  in  the  most  careful  possible 
preparation  of  the  eyeball,  for  the  effect  can  be  at  once 
reproduced  by  slightly  compressing  the  eyeball,  and  the  current 
aroused  by  such  intentional  manipulation  declines  just  like  the 
current  unavoidably  aroused  in  the  preparation  of  the  eyeball. 
So  much  for  the  normal  or  accidental  current,  which  is  de- 
creasingly  positive  and  increasingly  negative,  at  least  during 
the  first  hour  or  two  of  observation. 

§  14.  The  principal  fact. — We  may  now  proceed  to  the 
principal  part  of  the  experiment  as  first  made  by  Holmgren, 
and  subsequently  repeated  by  Dewar  and  MacKendrick,  Kuhne 
and  Steiner,  Fuchs,  and  many  others. 

The  eyeball  current  is  steady,  the  galvanometer  spot  is 
sinking  with  imperceptible  slowness  to  your  left,  and  I  expose 
the  eyeball  to  a  brief  flash  of  light  by  means  of  an  ordinary 
photographic  shutter  timed  at  about  ^-g-g-  second.  The  galvano- 
metric  spot  makes  a  small  excursion  to  your  right  (positive), 
indicative  of  a  current  through  the  eyeball  from  fundus  to 
cornea  in  response  to  the  flash  of  light.  The  direction  and 
character  of  this  response,  which  are  perfectly  normal,  are 
nearly  sufficient  to  assure  me  that  we  have  under  our  observation 
a  normal  and  well-prepared  eyeball,  but  I  shall  not  be  quite 
sure   of  this   until    I    have   seen   how  the   galvanometer   spot 

faces  east,  so  that  the  N  terminal  of  the  galvanometer  is  to  the  left  and  the 
S  terminal  to  the  right.  As  far  as  possible  the  connections  are  arranged  so 
that  currents  in  a  "positive"  or  "outgoing"  or  "ascending"  direction  shall 
give  deflections  to  the  right,  "  negative"  or  "ingoing"  or  "descending" 
currents  deflections  to  the  left. 


26 


THE  SIGNS  OF  LIFE 


[lect. 


behaves  itself  with  a  more  prolonged  exposure  of  the  eye.  So 
I  adjust  the  shutter  for  such  prolonged  exposure  to  light 
— a  minute  will  be  a  convenient  time — expecting  to  obtain, 
if  the  eyeball  is  quite  normal,  a  larger  and  increasing  posi- 
tive deflection  during  exposure.  And  now  watch  the  spot 
rather  closely  for  what  will  happen  when  I  cut  off  the  light  by 
closing  the  shutter ;  as  you  hear  the  click  of  closure,  you  see 
that  the  spot  makes  a  short  positive  excursion  to  your  right 
before  falling  back  to  its  original  starting  position.  All  these 
features  will  be  best  realised  from  a  photographic  record  of  the 
travelling  spot ;  here  is  such  a  record,  on  which  you  readily 
distinguish  the  large  positive  and  increasing  response  to  a 
prolonged  exposure,  ending  by  the  small  positive  response  or — 
as  we  fam-iliarly  call  it  in  the  laboratory — the  "parting  bow" — 


o  mins 


Fig.    IO. — Frog's    eyeball.       Galvanometric    record    of   five    successive 
normal  responses  to  light ;  each  illumination  lasts  for  one  minute. 

at  the  cessation  of  illumination,  after  which  the  current 
gradually  falls  to  its  original  level.  This  has  been  no  excep- 
tional result,  but  the  typical  and  regular  mode  of  response  of  a 
normal  careiully  prepared  eyeball ;  the  photographic  record  of 
five  such  responses  taken  on  a  more  slowly  travelling  plate  will 
be  sufficient  evidence  of  this.  In  each  case  there  is  deflection 
in  the  positive  direction  at  "  make  "  of  light,  during  light,  and 
at  "  break  "  of  licrht. 


15.  Furthci'  points, — There  are  several  subordinate  points 


n.J 


RETINAL  DELAY 


27 


relating  to  the  above  described  typical  positive  response  to  light 
that  demand  consideration.  I  will  deal  with  them  as  briefly  as 
possible.  In  the  first  place,  it  is  of  no  moment  as  regards  the 
response,  whether  the  accidental  current  described  in  paragraph 
13  happens  to  be  positive  or  negative.  Kiihne  and  Steiner, 
who  paid  particular  attention  to  the  point,  refer  to  the  fact 
under  the  heading,  Law  of  Constant  Alteration  of  Tension,  and 
describe  it  thus  : — 

"  Reversed  direction  of  the  current  of  darkness  (our  accidental 
current)  is  without  influence  upon  the  magnitude  and  character 
of  the  photo-electrical  variations,  which  reverse  their  signs."  That 
is  to  say,  according  to  the  German  designation,  that  the  response 
of  a  positive  current  of  darkness  is  in  the  same  direction  as  that 


^  sees. 

Fig.  II. — Frog's  eyeball.  Galvanometric  record  of  the  normal 
response  at  beginning  (a)  and  end  (w)  of  illumination.  '1  he  delay  in 
each  case  is  about  ^  sec.  ;  that  of  the  galvanometer  is  ^  sec.  ;  the  net 
retinal  delay  is  therefore  about  J  sec. 

current,  or  "positive,"  while  the  response  of  a  negative  current  of 
darkness  is  in  the  opposite  direction  to  that  current,  or  "  negative." 
I  have  preferred  to  this  correct,  but  rather  confusing  mode  of 
description,  to  say  that  the  response  is  normally  from  fundus  to 
cornea  or  positive,  whether  it  starts  above  or  below  the  line  of 


28 


THE  SIGNS  OF  LIFE 


[lect. 


zero  current,  i.e.,  whether  the  accidental  current  upon  which  it 
is  superposed  be  positive  or  negative.  Or  to  use  a  familiar 
laboratory  mnemonic — the  normal  excited  eyeball  always  "  looks 
through  its  own  galvanometer."     (See  Fig.  3). 

There  is  always  a  considerable  interval  of  time  between  the 
incidence  of  light  and  the  electrical  response ;  sometimes  the 
delay  at  "make"  of  light  may  be  so  great  as  to  be  measurable 
by  a  stop-watch,  but  in  such  cases  the  delay  at  "  break  "  is  much 
less  considerable,  and  I  have  considered  the  interval  at  make 
as  a  period  of  hesitation  iinde  infra)  rather  than  as  a  true 
physiological  lost-time.  But  even  under  the  most  favourable 
conditions,  with   fresh   and  typically  reacting   eyeballs,   I   have 


Fig.  12. — Frog's  eyeball.  Electrometric  record  of  the  normal  response  at 
beginning  (a)  and  end  (w)  of  illumination.  The  retinal  delay  is  in  each  case  about 
\  sec,  /.(?.,  approximately  the  same  as  that  of  cortical  grey  matter. 

never  seen  the  latency  as  short  as  given  by  Dewar  and 
MacKendrick,  and  more  recently  by  Fuchs — viz.,  "  less  than 
Y^xr^h  of  a  second."  The  shortest  intervals  I  have  measured 
have  been  of  about  \  second,  no  difference  being  detectable 
between  the  make  and  the  break  deflections  in  this  respect. 
These  values  have  been  obtained  from  galvanometer  records,  of 
which  Fig.  1 1  is  an  example,  and  are  subject  to  a  correction,  by 


II.]  .  THREE  TYPES  OF  RESPONSE  29 

reason  of  the  physical  lost-time  of  the  suspended  magnets  and 
mirror.  With  the  capillary  electrometer,  which  has  no  appreci- 
able lost-time,  the  latency  comes  out  at  about  0.15  second — still 
a  very  considerable  delay,  and  indicative  of  a  rather  surprising 
physiological  inertia  of  the  retinal  organ.*     (See  Fig.  12.) 

I  had  the  curiosity  to  repeat  the  experiment  under  precisely 
similar  conditions  on  an  oxidised  copper  plate,  which,  as  is  well 
known,  is  acted  upon  by  light,  and  gives,  therefore,  electrical 
currents  in  response  to  illumination  (Fig.  61,  p.  159).  There 
was  no  detectable  lost-time,  either  by  galvanometer  or  by 
electrometer — a  fact  which  is  of  interest  in  the  present  con- 
nection merely  in  that  it  bears  witness  to  the  correctness  of  the 
retinal  data  taken  by  the  same  apparatus. 

When  it  has  been  clearly  recognised  that  the  regular  and 
typical  response  of  the  fresh  uninjured  eyeball  is  of  positive 
direction,  i.e.,  directed  from  fundus  to  cornea,  we  may  proceed  to 
consider,  without  losing  our  way  amid  a  tangle  of  abnormalities, 
the  varieties  of  character  that  present  themselves,  not  merely  in 
the  response  to  light,  but  in  the  response  to  mechanical  and  to 
electrical  stimulation.  And  when  we  have  considered  such 
varieties,  we  shall  return  to  the  consideration  of  the  above 
described  typical  positive  response,  and  recognise  that  this  posi- 
tive response  is  in  all  probability  the  algebraic  sum  of  two 
opposite  and  not  perfectly  congruent  electrical  changes.  The 
terminal  positive  effect  at  the  closure  of  illumination,  which 
must  have  been  to  us  at  first  sight  a  somewhat  puzzling  feature, 
will  then  become  intelligible  to  us. 

§  16.  Three  types. — For  the  sake  of  distinct  description,  I 
have  classified  the  response  to  light  as  falling  into  one  or  other 
of  three  types  : — 

I.  Positive  response  of  the  first  type,  characteristic  of  the 
normal  fresh  uninjured  eyeball. 

II.  Mixed  responses, ,  characteristic  of  transitional  states 
between  types  I.  and  III. 

III.  Negative  response  of  the  third  type,  characteristic  of  the 
compressed  or  partially  injured  eyeball. 

*  Gotch  has  recently  and  independently  made  similar  observations  (see 
References). 


30 


THE  SIGNS  OF  LIFE 

Dark.  Light:. 


[lect. 


First  or  normal  type.         ''^Ol 


Second  or  transitional  q 

type. 


Third  or  reversed  type. 


■0003 


Dark. 


I  mm. 


am  ins 


Fig.  13. — Froy's  eyeball.     The  three  types  of  its  response  to  light, 
as  described  in  the  text. 


tl.] 


INFLUENCE  OF  MASSAGE 


31 


I  have  formed  the  opinion,  from  a  large  number  of  observa- 
tions and  trials,  that  the  principal  factor  in  bringing  about  that 


4- 

Tl .:■..., 

\, 

O  /  2  mins. 

Fig.  14. — Positive — before  massage. 


o  I  2l  mins. 

Fig.  14. — Negative- — after  massage. 

Response  to  light  (25  units).  The  horizontal  lines  in  both 
these  records  denote  a  scale  in  yTyi^prrths  of  a  volt ;  the  resistance 
of  the  eyeball  has  been  much  diminished  by  massage. 


state  of  eyeball  in  which  the  response  to  light  is  purely  negative, 
is  a  moderate  compression,  or  shrinking  by  drying  of  its  retinal 


32 


THE  SIGNS  OF  LIFE 


b 


coats.     A  fresh  eyeball  prepared  with  such  care  as  to  give  the 
typical  positive  response  of  the  first  type  can  at  once  be  made 


+ 


Fig.  15. — Diagram  to  illustrate  the  effect  upon  a  galvanometer 
(broken  line)  of  a  simultaneous  larger  positive  current  and  smaller 
negative  current,  the  latier  commencing  and  ending  more  rapidly. 


Fig.  15. — Retinal  response  of  the  second  stage,  illustrating 
the  double  effect. 


to  give  the  negative  response  of  the  third  type  by  gentle  massage 
or  by  steady  moderate  compression,  and  in  the  latter  case  it  is 


II.] 


PERIOD  OF  HESITATION 


33 


possible  with  very  gradual  compression  to  obtain  response  of 
the  transitional  type. 

The  conversion  of  type  I.  into  type  III.  by  means  of  gentle 
massage  forms  a  simple  and  almost  an  unfailing  lecture  demon- 
stration.    Fig.  14  is  the  record  of  a  case  in  point. 

^  ly.  A  double  process. — I  think  that  any  one  who  has  wit- 
nessed a  great  number  of  experiments  of  this  character,  and 
who  has  carefully  inspected  a  large  number  of  records  such  as 
those  figured  above,  will  be  forced  to  the  conclusion  that  the 
normal  positive  response  is  the  algebraic  sum  of  two  opposite 


Fig.  16. — Frog's  eyeball.     False  latent  period  or  period  of  hesitation 
in  this  instance  =  5  sees. 

and  almost  synchronous  electromotive  phenomena,  one  giving 
a  positive  current  that  over-compensates  the  other  giving 
negative  current ;  the  first  more  labile  than  the  second,  so  that 
by  gentle  compression  it  may,  so  to  say,  be  wiped  out,  and 
the  second  be  thus  unmasked. 

A  careful  scrutiny  of  the  manner  in  which  the  normal  positive 
response  begins  and  ends  confirms  this  view,  and  at  the  same 
time  offers  to  us  a  plausible  explanation  of  what  has  been  referred 

C 


34  THE  SIGNS  OF  LIFE  [lect. 

to  above  as  the  "  parting  bow."  If  during  the  exposure  to  Hght 
there  is  a  tug-of-war  between  positive  and  negative  current, 
with  predominance  of  the  former,  and  if  at  the  end  of  exposure 
both  currents  should  cease,  but  the  negative  cease  more  rapidly 
than  the  positive,  then  we  should  witness  what  actually  does 
happen,  viz.,  a  short  movement  in  the  positive  direction  preceding 
the  return  to  a  state  of  rest.  And  finally,  on  turning  back  to  the 
nicer  examination  of  the  rising  effect  at  the  outset  of  exposure, 
we  find  another  sign  of  an  opposition  between  two  contrary  and 
all  but  synchronously  developing  currents.  There  is  often  at  this 
point  a  false  latent  period,  or  period  of  hesitation,  perceptible  on 
simple  observation,  or,  better  still,  by  means  of  records  where 
the  beginning  of  an  exposure  has  been  mechanically  signalled, 
amounting  to  several  seconds,  and  intelligible  only  on  the  sup- 
position that  our  galvanometric  magnet  is,  so  to  say,  trembling 
in  the  balance  between  two  opposite  and  almost  perfectly  con- 
gruent forces.  And  generally,  indeed,  on  the  record  of  such  a 
false  latent  period,  we  may  detect  signs  of  such  a  preliminary 
struggle,  as  if  an  initial  positive  movement  had  been  forthwith 
interfered  with  for  a  brief  period  by  a  contrary  negative  move- 
ment. On  some  records  the  magnet  remains  almost  perfectly  at 
rest  during  several  seconds  of  hesitation ;  on  others  it  is  caught 
back  by  a  sharp  negative  jerk  ;  on  others  still  the  curve  of  positive 
movement  is  only  slightly  hitched  or  notched  in  its  progressive 
development.  All  these  facts — viz.,  the  transitional  responses 
from  positive  to  negative,  the  immediate  conversion  from  positive 
to  negative  by  compression,  the  initial  period  of  hesitation,  the 
terminal  "  parting  bow  " — point  to  one  and  the  same  conclusion, 
viz.,  that  the  retina,  when  exposed  to  light,  is  the  seat  of  two 
contrary  electro-motive  changes.  And  it  matters  little  whether 
you  imagine  two  single  processes  or  one  double  process  behind 
the  movements  of  the  machinery. 

Thus,  following  a  path  step  by  step  as  it  happens  to  lead  us, 
we  find  ourselves  quite  unexpectedly  at  a  place  where  theory 
and  doctrine  seem  to  be  quite  familiar  to  us.  We  are  all  of  us 
more  or  less  intimately  acquainted  with  Hering's  theory  of 
colour-vision  setting  forth  that  contrary  processes  of  dissimila- 
tion and  assimilation   are   aroused   by  complementary  colours, 


II.]  COLOURED  LIGHT  35 

white  and  black,  red  and  green,  yellow  and  blue.  And  whether 
or  no  we  happen  to  believe  that,  e.g.,  a  red  light  is  katabolic  and 
a  green  light  anabolic,  we  assuredly  do  believe  in  what  has  been 
termed  by  Bernard  the  axiom  of  general  physiology — that 
katabolic  analysis  and  anabolic  synthesis  are  inconceivable  apart 
from  each  other.  I  think  that  we  should  not  hastily  admit  that 
our  double  electrical  change  is  presenting  us  to  another  aspect 
of  a  familiar  if  somewhat  nebulous  colour  theory ;  I  think  we 
have  no  ground  for  assuming  that  our  conclusion  means  any- 
thing more  than  the  old  axiom  behind  a  new  face.  A  process 
necessitates  the  anti-process,  and  if  the  process  is  attended 
by  an  electrical  change  of  given  sign,  we  may  expect  that 
the  anti-process  will  entail  an  electrical  change  of  opposite 
sign.  The  chemical  changes  taking  place  in  living  matter  are 
in  general  reversible  changes. 

§  1 8.  Complementary  colours. — One  question  we  may  indeed 
put  to  the  test  before  passing  on.  We  may  see  whether  or 
no  complementary  colours  have  opposite  electrical  effects,  and 
whether  the  excessive  action  of  a  given  colour  favours  or  dis- 
favours the  action  of  its  complementary.  I  have  tried  both 
these  points ;  I '  had  no  real  expectation  that  red  and  green 
light,  e.g.,  should  have  electrical  effects  of  opposite  signs,  nor 
that  the  excessive  action  of  a  given  monochromatic  light  would 
promote  the  subsequent  action  of  its  complementary.  And  in 
point  of  fact,  neither  of  these  things  happened.  The  effects 
of  all  sorts  of  colours  were  of  the  same  sign.  The  joint  effect 
of  two  complementary  colours  was  practically  the  sum  of  their 
separate  effects.  And  the  prolonged  excessive  action  of  a 
given  colour  fatigued  the  retina  to  that  colour  just  as  much  or 
as  little  as  to  the  complementary  colour.  All  colours,  in  fact, 
as  regards  the  electrical  response  they  elicit  from  the  retina, 
give  that  response  of  the  same  sign,  and  seem  to  act  in  the  same 
direction,  more  or  less  powerfully  according  as  they  are  more 
or  less  luminous.  Thus,  e.g.,  in  a  given  series  of  trials,  the 
responses  came  out  of  the  following  relative  magnitudes  : — 

Green   .         .         .  +12 


Red        .         .         .  +4 

Yellow   .         .         .  +16 

(White).         .         .  +33 


Blue     .         .         .         +9 


36  THE  SIGNS  OF  LIFE  [lect. 

In  other  trials  the  responses  were  : — 

To  Red  alone  .  +5  I         To  Red  and  Green  conjoined  + 14 

To  Green  alone       .  +10  1         (To  White)     .         .         .  +40 

§  19.  Cause :  effect. — I  have  upon  more  than  one  occasion 
taken  records  of  the  series  of  electrical  effects  elicited  by  a 
series  of  illuminations  of  arithmetically  increasing  and  de- 
creasing strengths.  The  general  question  to  which  this  special 
question  belongs  is  in  my  opinion  one  of  fundamental  elemen- 
tary importance,  coming  under  our  notice  in  almost  every  pro- 
vince of  study,  sometimes  in  simple  and  accessible  shape, 
sometimes  disguised  or  hidden  by  the  manifold  circumstances 
and  accessories  of  organic  life. 

The  question  is  :  What  quantities  of  physiological  effect,  Y, 
are  elicited  by  given  quantities  of  physical  cause,  X  ?  And  the 
answers  to  that  question  in  its  various  forms  will  be  most 
conveniently  and  symmetrically  expressed  by  a  curve  to  the 
co-ordinates  OX,  OY,  with  the  physical  cause  or  stimulus  or 
excitation  plotted  along  OX,  and  the  physiological  effect 
along  OY. 

Generally  speaking,  we  cannot  hope  to  reach  in  physiological 
matters  an  accuracy  such  as  is  possible  in  physical  matters. 
Our  data  are  too  rough,  perturbed  by  too  many  uncontrollable 
variables,  and  may  not  as  a  rule  be  formulated  in  mathemati- 
cally correct  curves  characterised  by  simple  equations.  The 
well-known  logarithmic  law  of  sensation  is  at  best  of  very 
limited  application,  and  a  sensation  curve  actually  plotted  from 
experimental  data  exhibits  great  divergences  from  any  loga- 
rithmic curve  that  can  be  fitted  to  it.  Without,  however,  making 
any  attempt  to  trim  or  strain  experimental  results  and  fit  them 
with  orthodox  mathematical  curves,  we  may  with  advantage 
plot  them  out  to  scale  on  a  simple  system  of  co-ordinates  OX, 
OY,  and  thus  recognise  at  a  glance  whether,  within  the  range  of 
the  observations  made,  a  given  physiological  effect  has  varied 
(i)  as  its  cause,  or  (2)  more  rapidly  than  its  cause,  or  (3)  less 
rapidly  than  its  cause.  I  mean  of  course  exciting  or  proximal 
efficient  cause  or  stimulus,  and  not  the  whole  previous  chain  of 
principiants  resulting  in  the  particular  event. 


tij  -  CAUSE  :  EFFECT 

Let  us  consider  the  three  cases  : — 

y  y  y 


S7 


Fig.  17.— Straight. 


The  effect  Y  varies  as  its 
cause  X. 

Equal  increments  of  cause 
produce  equal  increments  of 
effect.  The  cause/ effect  cuiTe 
is  a  straight  line. 


Concave. 

The  effect  T  varies  more 
rapidly  than  its  cause  X. 

Equal  increments  of  cause 
produce  increasing  incre- 
ment of  effect.  The  cause  / 
effect  curve  is  convex  to  its 
abscissa  OX. 


Convex. 


The  effect  Y  varies  less 
rapidly  than  its  cause  X. 

Equal  increments  of  cause 
produce  diminishing  increments 
of  effect.  The  cause  /  effect 
curve  is  concave  to  its  abscissa 
OX. 


And  now  turn  to  the  case  in  point,  where  the  cause  X  is  the 
intensity  of  a  light,  and  the  effect  Y  the  magnitude  of  a  galvano- 
metric  deflection  (which  we  shall  assume  to  measure  magnitude 
of  electrical  change,  and  therefore  magnitude  of  retinal  change). 
With  a  light  of  suitable  strength,  varied  on  an  arithmetic 
scale  constructed  in  conformity  with  the  law  that  luminosity 
varies  inversely  as  the  distance  squared,  we  find  the  following 
series  of  results  from  the  given  series  of  stimuli : — 

Stimulation  by  light    .         2         4         6         8         10  X 
Retinal  change     .         .       208     248     274     296     326  Y 

which,  plotted  as  described  above,  gives  the  curve  figured  below 
as  that  of  the  retinal  effects  of  medium  illumination. 


, 

)        5        ! 

1       2       \ 

)        J 

\     J 

Units  qP       ...       , 
eccciCabion.     Weak. 


Medium. 


-!       !' 


Strong. 


20     40     60     ao     100 


Fig.  18. — Frog.  Retinal  response  to  illumination  of  constant  duration  and  of 
varying  strength.  The  unit  of  light  is  a  standard  candle  at  a  distance  of  lo  feet  from 
the  eyeball. 

Now  this  curve,  concave  to  its  abscissa  OX,  with  the  effect 
Y    increasing    less    rapidly  than    its    excitant    cause    X,  is   in 


38  THE  SIGNS  OF  LIFE  [lect. 

conformity  with  almost  every  series  of  observations  we  are  able 
to  carry  out  on  living  matter.  The  familiar  logarithmic  curve 
of  sensation  is  concave  to  its  abscissa,  sensation  Y  increases  by 
diminishing  increments  for  equal  increments  of  stimulation  X. 
Muscular  contraction,  the  negative  variation  of  a  nerve-current 
(as  I  have  shown  previously),  give  the  same  type  of  curve  within 
at  least  a  certain  range  of  observation.  And  other  cases  might 
be  quoted  illustrating  the  general  law,  that  the  response  of  living 
matter  to  the  excitation  of  its  environment  increases  by  dimish- 
ing  increments,  giving  a  cause/effect  curve  that  is  coiicave  towards 
its  abscissa.  And  we  need  not  attempt  to  see  whether  or  no 
this  curve  can  be  neatly  fitted  with  a  logarithmic  formula,  for 
the  fit  or  the  misfit  of  a  curve,  constructed  from  such  a  formula, 
would  not  afford  much  information  beyond  what  is  to  be  learned 
from  inspection  of  the  empirical  curve,  and  comparison  with 
other  curves. 

Moreover,  one  may  convince  himself  at  once  by  somewhat 
closer  observation,  that  the  entire  range  of  any  given  cause/ 
effect  curve  cannot  be  fitted  by  a  logarithmic  formula.  Above 
the  range  of  moderate  stimulation,  we  have  no  further  increment 
of  effect,  but,  on  the  contrary,  a  decrement,  attributable  to  fatigue 
or  to  shock,  or  to  actual  injury  by  excessive  stimulation.  And 
below  the  range  of  moderate  stimulation,  the  curve  does  not 
spring  suddenly  from  its  abscissa  and  rise  by  increments  diminish- 
ing from  the  very  outset,  but  it  rises  gradually  from  zero  by 
increments  smallest  at  first  then  increasing,  so  that  a  first  part 
of  the  curve  instead  of  concave  is  convex  to  the  abscissa,  and  the 
whole  curve  S-shaped,  convex  at  first,  concave  at  a  higher  range. 
I  have  urged  elsewhere  that  this  S-shaped  character  of  the 
cause/effect  curve  is  general,  and  that  any  well-studied  case, 
where  we  can  plot  physical  cause  along  an  abscissa  and  physio- 
logical effect  along  ordinates,  will  probably  be  found  to  yield 
such  an  S-shaped  curve.* 

§  20.  AncBstJietics. — In  conclusion  of  this  chapter  I  will 
briefly   remark    on    the    two    last  headings    of  the  syllabus   in 

*  Waller. — "  On  the  Excitability  of  Nervous  Matter."  Presidential 
Address  to  the  Neurological  Society,  1900.     Brain,  1900. 


II.]  -  ANESTHETICS  39 

your  hands ;  one  of  these — the  action  of  anesthetics — I  took 
the  opportunity  of  examining  with  some  care  a  few  years  ago 
in  connection  with  a  methodical  study  of  the  action  of  anaes- 
thetics on  isolated  nerve  ;  *  the  other — retino-motor  effects — I 
have  not  worked  at  myself;  it  rests  upon  the  authority  of 
Engelmann,  who  discovered  and  worked  the  point  with  his 
pupil  Grijns. 

The  ordinary  anaesthetics — carbon  dioxide,  ether,  and  chloro- 
form— influence  the  electrical  response  of  the  retina  to  light  as 
might  be  expected  from  a  consideration  of  the  physiological 
character  and  conditions  of  the  response  and  the  relative  power 
of  the  anaesthetics  used.  With  an  enucleated  eyeball  as  the 
object  of  experiment,  the  layer  to  be  anaesthetised  is  compara- 
tively well  protected  by  the  sclerotic  coat,  and  the  effects  of  an 
anaesthetic  vapour  are  obstructed  if  only  because  its  access  to 
the  retina  is  obstructed.  Still  the  characteristic  effects  of  the 
three  anaesthetics  are  produced,  although  more  slowly  and  im- 
perfectly than  in  the  case  of  an  isolated  nerve.  Carbon  dioxide 
gives  diminution  followed  by  augmentation  of  the  response. 
Ether  gives  temporary  diminution  or  abolition  of  the  response, 
followed  (usually)  by  perfect  recovery.  Chloroform  gives  aboli- 
tion of  the  response,  and  the  abolition,  once  it  is  produced,  is  apt 
to  be  final. 

§  21.  Retino-motor  effects. — The  effects  studied  by  Engel- 
mann and  Grijns  are  interesting  in  two  chief  particulars  :  they 
indicate  the  possible  existence  of  efferent  fibres  in  that  most 
typical  afferent  nerve,  the  optic  nerve  (retino-motor)  ;  and  they 
afford  some  answer  to  a  question  that  has  no  doubt  occurred 
to  you,  whether,  namely,  the  electrical  change  occurring  in  an 
illuminated  retina,  belongs  to  altered  pigment  or  to  retracted 
cones  or  to  both  phenomena.  The  chief  points  in  Engelmann's 
observations  are,  that  retraction  of  the  cones  and  an  electrical 
effect  can  be  produced  in  one  eye  by  electrical  excitation  of 
the  peripheral  end  of  its  optic  nerve,  or  of  the  central  end  of 

*  Waller. — "  The  Action  of  Ansesthetics  on  Nerve."  Presidential 
Address  to  the  Section  of  Anatomy  and  Physiology  of  the  British  Medical 
Association.     Montreal,  1897.     British  Medical  Journal,  1897. 


40  THE  SIGNS  OF  LIFE  [lect.  ii. 

the  other  optic  nerve,  or  by  luminous  stimulation  of  any  part  of 
the  skin.  I  think  we  are  bound  to  accept  as  correct  the  results 
vouched  for  by  an  observer  of  Engelmann's  experience,  yet,  I 
must  confess,  that  I  cannot  defend  myself  from  a  lingering 
doubt  when  I  remember  how  sensitive  the  retina  may  be  to 
the  weakest  trace  of  light  (I  have  seen  distinct  reaction  to 
a  flash  of  moonlight  lasting  x^th  second,  and  quite  recently,  by 
courtesy  of  Sir  W.  Crookes,  to  the  luminosity  of  radium),  and 
when  I  consider  how  difficult  it  must  be  to  absolutely  protect 
an  eye  from  all  trace  of  direct  illumination,  while  sunlight  is 
reflected  on  to  the  other  eye  or  on  to  the  skin. 


REFERENCES 


Holmgren. — "Ueber  die  Retinastrome,  Cdf. /.  d.  fned.  Wissettsch."  1871; 

p.  423- 
Dewar  and  MacKendrick. — "On  the  Physiological  Action   of    Light," 

Trans.  Roy.   Soc,  Edinburgh,   1873,  p.    141;  and, /ozim.  0/ Anat.  and 

Physiol.,  vii.,  1873,  p.  275. 
Kuhne  and  Steiner.— I.    "  Ueber  das  Electromotorische  Verhalten  der 

Netzhaut,"  II.  "Ueber  Electrische  Vorgange,"  U?iters.  a.  d.  Physiol.  Inst. 

Heidelberg,  iii.  and  iv.,  1 880-1 881. 
Beck. — "  Ueber  die  bei   Belichtung  der  Netzhaut  von  Elodone  moschata 

entstehenden  Actionstrome,"  Pfliiger's  Archiv.  Ixxviii.,  1899,  p.  129. 
FUCHS. — "  Untersuchungen  iiber  die  im  Gefolgeder  Belichtung  auftretenden 

galvanischen    Vorgange    in  der    Netzhaut    und  ihren    zeitlichen  Ver- 

lauf,"  Pfiiiget^s  Archiv.,  Ivi.,  1894,  p.  408. 
Waller.—"  On  the  Retinal  Currents  of  the  Frog's  Eye,  excited  by  Light,  and 

excited  Electrically,"  Phil.  Trans.  Roy.  Soc,  B  vol.  193,  1900,  p.  123. 
Waller. — "  On  the   Blaze-Currents   of  the  Frog's    Eyeball,"  Phil.  Trans. 

Roy.  Soc,  B  vol.  194,  1901,  p.  183. 
Waller. — "The   Eyeball  as   an   Electrical   Organ,"   Proc   Physiol.   Soc, 

10  November  1900. 
Engelmann  and  Gruns. — Belmholfz'  Festschrift,  1891. 
GOTCH. — "  The  Time-Relations  of  the  Photo-Electric  Changes  of  the  Eye- 
ball of  the  Yrog,^^  Journ.  of  Physiol.,  vol.  xxix.,  1903,  p.  388. 


LECTURE  III 

Plan  of  this  Lecture — Electrical  Excitation  of  a  Frog's  Eyeball — Modifica- 
tion of  the  Response  to  Light  subsequent  to  Tetanisation,  and  during 
Tetanisation — Effects  and  After-effects  of  Single  Shocks — "  Blaze- 
currents" —  Polarisation  Currents  —  Electrocution  —  Three  Types  of 
Blaze-currents — The  Effect  is  greater  than  its  Cause — Influence  of  a 
talvanic  Current — Some  Questions — The  Crystalline  Lens. 

§  22.  I  propose  to  consider  to-day,  and  as  much  as  possible 
demonstrate : — 

1.  The  effects  and  after-effects  of  tetanisation  upon  the 
eyeball. 

2.  The  influence  of  tetanisation  upon  its  electrical  response 
to  light. 

3.  The  influence  of  light  upon  the  electrical  effects  of  elec- 
trical shocks. 

4.  The  effects  and  after-effects  of  single  induction  shocks 
(and  of  condenser  discharges)  upon  the  eyeball ;  and 

5.  The  influence  of  galvanic  currents  on  the  effects  of 
induction  shocks. 

No  small  undertaking  indeed  for  a  single  day's  work, 
nevertheless  one  that  we  shall  hope  to  meet  by  aid  of  a  series 
of  simple  experiments.  Of  course  I  well  know  that  a  string 
of  experiments,  perfectly  successful  it  may  be,  but  imperfectly 
explained  and  understood,  has  equal  value  with  a  string  of  con- 
juring tricks,  but  I  take  it  that  by  this  time  you  see  your  way 
through  the  apparatus  set  out  on  the  lecture  table  and  the 
diagrams  hung  at  your  elbow.  Moreover,  I  can  refer  you  to  a 
paper  published  last  year,  on  the  Blaze-currents  of  the  Frog's 
Eyeball,  that  contains  at  greater  length  than  would  be  suitable 
for  a  lecture  the  results  and  considerations  that  we  are  about  to 
review.     I  venture  to  think  that  the  reading  of  the  paper  would 

41 


42 


THE  SIGNS  OF  LIFE 


[I 


help  you  to  understand  the  lecture,  and  that  the  hearing  of  the 
lecture  may  help  you  to  understand  the  paper. 

§  23.  The  effects  of  tetanisation.     Experiment  I. — When  one 
has  seen  that  the  stimulation   of  an  eyeball  by  light  arouses 


--^-  Ughb. 


/nductorium. 


Fig.  19. — Frog's  eyeball  between  unpolarisable  electrodes  for  demonstration  of 
the  electrical  effects  of  light  and  of  electrical  excitation.  The  circuit  from  the  eye  is 
completed  through  a  compensator,  secondary  coil,  and  galvanometer.  The  arrows 
through  the  eyeball  and  the  galvanometer  indicate  the  direction  of  the  initial  current 
and  of  the  normal  response.  Arrows  near  the  compensator  wires  indicate  the  direction 
of  compensating  counter-current. 


a  positive  electrical  response  (and  that  any  mechanical  dis- 
turbance arouses  current  in  the  same  direction),  he  naturally 
thinks  of  electrical  excitation,  and  expects  to  find  that 
if  the  retina  is  stirred  up  to  activity  by  such  means,  it  will 
manifest   current   in   that   same    positive   direction.      The   ex- 


iiT.]  -  TETANISATION  43 

pectation  is  realised  by  the  following  experiment,  in  which, 
as  you  will  readily  see  from  the  diagram,  a  weak  tetanising 
current  is  to  be  passed  through  a  secondary  coil,  an  eyeball, 
and  a  galvanometer,  all  the  plugs  being  removed.  The 
tetanising  current  is  so  weak  that  its  constituent  single  shocks, 
alternating  in  direction,  do  not  of  themselves  affect  the  gal- 
vanometer, but  do  stimulate  the  eyeball,  which  gives  current 
in  the  circuit,  current  which,  as  you  see  from  the  deflec- 
tion of  the  spot  to  your  right,  is  in  the  expected  (positive) 
direction. 

I  repeat  the  experiment,  having  turned  over  a  reverser  in 
the  secondary  (or  it  might  have  been  in  the  primary)  circuit, 
in  order  to  reverse  the  directions  of  the  constituent  shocks, 
and  the  spot  is  again  deflected  to  your  right.  I  take  it  that 
this  experiment  needs  no  comment ;  it  says  that  induction 
currents  of  both  pairs  of  directions  arouse  a  positive  electrical 
response  of  the  eyeball. 

In  ordinary  language,  the  "effect"  of  a  modifying  cause  is 
subsequent  to  that  cause,  and  is  therefore,  properly  speaking,  an 
"  after-effect."  But  it  is  in  some  instances  necessary  to  distinguish 
between  the  effect  during  its  cause,  and  the  after-effect  subse- 
quent to  that  cause.  You  have  just  witnessed  the  effect  during 
tetanisation  —  necessarily  during  weak  tetanisation.  I  cannot 
show  you  an  effect  during  strong  tetanisation,  since  strong 
induction  currents  traversing  the  galvanometer  would  mask  the 
physiological  current  of  the  eyeball.  If  you  should  wish  to 
observe  the  effects  of  strong  tetanisation,  you  must  be  content 
with  what  are  properly  speaking  after-effects,  since  I  must  put 
the  galvanometer  out  of  circuit  during  tetanisation,  and  unplug 
it  to  receive  the  eyeball  current  that  may  be  present  as  the  effect 
or  after-effect  of  strong  tetanisation.  And  I  will  do  this  now,  to 
show  that  the  effect  (or  after-effect)  of  tetanisation  may  be  very 
great  indeed.  The  eye  current  is  exactly  compensated  so  that 
I  can  plug  and  unplug  the  galvanometer  without  disturbing  the 
spot.  I  plug  the  galvanometer  and  tetanise  the  eyeball.  Then 
I  unplug  and  the  spot  flies  off  scale  to  your  right,  indicating 
positive  current  in  the  eyeball  as  an  effect  (or  after-effect)  of  the 
tetanisation. 


44 


THE  SIGNS  OF  LIFE 


[LECt. 


§  24.  The  effects  of  tetanisation  upojt  the  effects  of  light. 
Experiment  II. — Our  next  experiment  is  to  show  that  the 
electrical  response  to  light  is  modified  by  tetanising  cur- 
rents. I  had  to  use  very  weak  currents  for  the  first  ex- 
periment, I  shall  use  much  stronger  currents  for  this  one, 
because  I  want  to  show  an  unmistakable  modification  of  the 
electrical  response  to  light,  and  I  may  use  strong  currents  if 
while  they  are  passing  they  are  short-circuited  from  the  gal- 
vanometer. First  notice  the  response  to  light,  it  is  about  +14 
degrees  of  scale.  Now,  I  plug  out  the  galvanometer  and  tetanise 
the  eyeball  for  half  a  minute.  I  then  unplug,  and  the  spot  has 
flown  off  scale  to  your  right.  That  has  been  what  on  first 
witnessing  it  I  called  a  blaze-current ;  it  has  been  provoked  by 
the  tetanisation  to  which  the  eyeball  has  just  been  subjected. 
But  for  the  present  it  is  not  our  principal  concern.  I  bring  the 
spot  back  on  to  scale  by  means  of  a  compensating  current, 
and  as  soon  as  the  spot  has  come  to  comparative  rest — it  has 
been  gradually  falling  off  to  the  left  by  reason  of  the  gradual 
subsidence  of  the  blaze-current — we  again  take  a  reading  of  the 
electrical  response  to  light  ;  it  is  now  30  as  compared  with  14, 
its  value  before  tetanisation,  i.e.,  the  normal  response  to  light 
has  been  more  than  doubled  in  consequence  of  tetanisation. 


/ 
ipoo 


T,  (3,000) 


[Ia^-^ 


1_  20mins. 


O  5  lOmins.  0  \_         L-^     L        \!P       L     '-^  L 

Before  bet,anisa.bion.  After  bebanisd-Uon. 

Fig.  20. — Frog's  eyeball.  Influence  of  tetanisation  upon  the  normal  retinal 
response  to  light.  Ordinary  arrangement  of  induction  coil,  fed  by  two  Leclanche  cells. 
Secondary  coil  at  9  centims.  (5000  units  on  Berne  scale).  After  tetanisation  the 
positive  response  is  considerably  augmented,  and  falls  during  illumination.  The 
terminal  positive  deflection  at  break  of  light  is  almost  completely  abolished. 

This  marked  augmentation  of  response  as  to  czin^ent  may  be 
due  to  augmentation  oi voltage  or  oi conductivity, ox  to  both  factors; 


ni.J  SINGLE  INDUCTION  SHOCKS  45 

as  a  matter  of  fact  it  is  due  to  both  factors,  the  electro-motive 
force  of  the  response  is  increased,  and  the  resistance  of  the  eye- 
ball is  diminished.  You  will  recognise  both  these  points  on  the 
accompanying  record,  where  the  tetanisation  has  raised  the 
voltage  of  the  response  from  about  2wu"  to  nearly  xoW  5  you 
notice  also  that  the  standard  deflection  by  i^jV^  volt  has  been 
evidently  increased  —  indicating  increased  conductivity,  z>., 
diminished  resistance. 

§  25.  In  the  experiment  just  made  you  have  witnessed  a 
marked  effect  subsequent  to  tetanisation  ;  a  similar  effect  is 
witnessed  during  tetanisation,  but  it  is  rather  more  troublesome 
to  demonstrate  properly,  and  I  have  not  therefore  included  it  in 
to-day's  list.  I  will  content  myself  with  quoting  the  results  of 
a  former  experiment  in  which  the  deflections  in  response  to 
light  were  : — 

Before  tetanisation  12  degrees  of  scale. 
During  tetanisation  36  degrees  of  scale. 
After  tetanisation  27  degrees  of  scale. 

I  26.  The  effects  of  single  shocks.  Experiment  III. — The 
very  strong  currents  that  you  have  just  witnessed  as  after- 
effects of  strong  tetanisation  are — as  I  hope  to  prove  to 
you  in  a  future  lecture — in  chief  part  of  physiological  origin, 
but  in  minor  degree  merely  the  physical  effects  of  ordinary 
polarisation.  Their  experimental  analysis  is  a  complicated 
matter  that  cannot  profitably  be  dealt  with  before  we  have 
become  familiar  with  the  less  complicated  results  of  excita- 
tion by  single  induction  shocks  and  by  condenser  discharges. 
And  since  for  the  purpose  of  our  third  experiment  it  is  indifferent 
which  of  these  two  forms  of  electrical  excitation  we  may  choose 
to  take,  I  will  use  the  more  familiar  apparatus,  to  show  the  effects 
and  after-effects  of  a  single  break  induction  shock,  first  in  one 
and  then  in  the  other  direction.  You  understand,  of  course,  that 
the  expressions  "  effect "  and  "  after-effect "  are  simply  used  to 
distinguish  between  the  two  experimental  cases,  where  (i)  the 
induction  shock  and  the  response  are  allowed  to  pass  through 
the  galvanometer ;  and  (2)  only  the  response  is  allowed  to  pass, 


46  THE  SIGNS  OF  LIFE  •  [lect. 

the  induction  shock  (and  first  part  of  the  response)  occurring 
while  the  galvanometer  is  plugged. 

It  will  be  most  convenient  if  we  make  a  first  pair  of  trials  to 
witness  the  after-effects  of  two  single  break  induction  shocks  in  -!- 
and  —  directions. 

It  is  necessary,  in  first  place,  to  get  rid  of  the  make  induction 
shock.  You  will  readily  see  by  reference  to  the  diagram  how 
this  is  done.  The  primary  circuit  of  the  inductorium  is  closed 
by  a  spring  key,  and  while  this  is  done,  the  secondary  coil  is 
short-circuited  at  the  keyboard  (see  Fig.  19,  p.  42).  Then  this 
plug  is  removed  and  the  spring-key  released  so  that  a  break 
induction  shock  is  passed  through  the  eyeball.  And  finally  the 
galvanometer  plug  is  removed,  so  that  the  current  (if  any) 
aroused  in  the  eyeball,  traverses  the  galvanometer  and  deflects 
its  spot.  These  steps  are  quite  automatically  made  after  a  little 
practise,  and  at  a  quite  sufficiently  uniform  rate ;  the  electro- 
motive response  of  the  eyeball  is  so  prolonged  that  it  is  not 
necessary  to  hurry ;  although  obviously  for  comparative  trial  it 
is  preferable,  as  well  as  more  convenient,  to  use  a  special  key 
that  breaks  short-circuit  of  the  galvanometer  at  a  regular  interval 
{e.g.,  iVth  sec.)  after  breaking  the  primary  circuit.*  It  is  evident 
that  in  order  to  plug  and  unplug  the  galvanometer  without  dis- 
turbing its  spot,  all  current  in  circuit  must  be  compensated. 
This  compensation  has  been  adjusted  at  the  outset,  and  must 
be  exactly  re-adjusted  before  each  trial.  Then  we  shall  be 
assured  that  a  given  deflection  is  in  reality  due  to  current 
aroused  by  excitation,  and  not  to  any  accidental  current  in 
circuit. 

I  may  now  proceed  with  the  experiment.  I  begin  by  testing 
the  compensation,  and,  if  necessary,  adjusting  it.  I  then  send  a 
break  induction  shock  through  the  eyeball  in  the  negative 
direction,  and  afterwards  unplug  the  galvanometer.  The  spot 
flies  off  scale  to  your  right.  That  has  been  a  blaze-current,  of 
positive  direction  in  response  to  an  induction  shock  of  negative 
direction ;  it  is  not  a  polarisation  current ;  although  at  first 
sight  by  reason  of  its  direction  it  might  have  been  set  down  as 

*  See  Appendix,  Fig.  68,  p.  166. 


in.l 


BLAZE-CURRENTS 


47 


such ;  I  characterise  it,  in  distinction  from  the  next  variety  of 
current  that  you  will  witness,  as  equivocal  or  antidrome.  The 
current  is  subsiding,  rapidly  at  first,  now  more  gradually,  and 
more  and  more  so  as  the  spot  approaches  its  zero  position,  some- 
times, indeed,  we  may  witness  a  permanent  positive  deflection,  a 
current-remainder  reminding  one  of  the  contraction-remainder 
of  muscle. 

I  will  now  test  the  eyeball  by  an  induction  current  in  the 


Vobb 


mins.  10 

B  -  zooo 


J~j  •^  BOOO 


Fig.  21. — Normal  blaze-currents  of  a  frog's  eyeball  in  response  to  excitation  by 
a  single  break  induction  current  in  the  negative  or  antidrome  direction  (B  -  2000), 
and  in  the  positive  or  homodrome  direction  (B  +  2000). 

positive  direction  ;  so  I  adjust  the  compensation  and  turn  a 
reverser  in  the  induction  circuit,  send  a  break  induction  shock 
through  the  eyeball  in  the  positive  direction,  and  unplug  the 
galvanometer.  The  spot  flies  off  to  your  right  as  before.  That 
also  has  been  a  blaze-current,  of  positive  direction  in  response  to 
an  induction  shock  of  positive  direction  ;  it  is  evidently  not  a 
polarisation  current ;  I  characterise  it  in  distinction  from  the 
first  variety  as  unequivocal  or  homodrome. 

This,  in  my  opinion,  is  a  cardinal  experiment,  and  when  it 
was  deciphered,  became  sign-post  as  well  as  hinge  of  further  and 
more  general  investigation. 

But  let  us  complete  the  experiment.  The  eyeball — upon 
which  you  saw  a  moment  ago  that  two  very  large  responses  in 
one  and  the  same  direction  followed  excitation  by  single  break 
shocks  first  in  one  and  then  in  the  opposite  direction — has  been 
plunged  into  hot  water,  i.e.,  killed  and  replaced  between  the 
electrodes.  I  repeat  the  test  of  a  right  and  left  induction  shock 
and  no  movement  whatever  of  the  galvanometer  spot  is  to  be 
detected.     The  dead  eyeball  gives  no  blaze-current. 


48  THE  SIGNS  OF  LIFE  [lect. 

§  27.  Polarisation. — But  I  have  been  using  the  galvanometer 
"  at  low  power,"  much  shunted,  in  the  knowledge  that  the  blaze- 
currents  in  the  main  experiment  would  be  very  strong.  And  to 
see  whether  or  not  there  is  any  trace  of  response,  a  "  high  power  " 
of  the  galvanometer  must  be  taken  by  unshunting  it.  Which 
has  now  been  done  (and  you  notice  by  the  way  that  an  exact 
compensation  is  a  little  more  troublesome  to  effect),  and  I  repeat 
the  test,  right  and  left.  There  is  just  a  trace  of  after-effect — to 
your  left  (  — )  after  excitation  to  your  right  (  +  ),  to  your  right 
(-1-)  after  excitation  to  your  left  (  — ) — and  this  is  not  a  physio- 
logical response,  it  is  only  the  ordinary  polarisation  counter- 
current  exhibited  by  any  electrolyte.  I  will  show  it  you  in 
more  pronounced  form  with  a  couple  of  wires  dipping  in  salt 
solution,  but  not  now — after  lecture,  when  I  shall  also  test 
these  unpolarisable  electrodes.. 

§  28.  Experiment  IV. — You  have  just  witnessed  the  third 
experiment  in  one  form,  demonstrating  to  you  physiological 
after-effects,  and  you  will  have  no  difficulty  now  in  following 
the  steps  by  which  I  am  about  to  make  it  in  another  form,  to 
demonstrate  to  you  these  same  after-effects  inclusive  of  their 
earliest  visible  manifestations,  which  I  have  referred  to  as  the 
effects.  I  do  not  think  that  the  distinctive  words  are  justified 
by  any  distinction  of  phenomena ;  their  use  has,  however,  been 
pressed  upon  me  by  the  necessity  of  distinguishing  between 
the  results  of  two  methods. 

A  fresh  eyeball  (that  has  just  been  tested  by  the  assistant 
and  found  to  respond  normally  to  light)  is  set  up  between  elec- 
trodes, and  I  intend  to  send  through  it  and  through  the  gal- 
vanometer a  break  induction  shock  of  suitable  strength,  first  in 
one,  then  in  the  other  direction.  The  strength  taken  as  suitable 
is  one  that  gives  through  a  circuit  of  resistance  equal  to  that 
formed  by  eyeball  electrodes  and  galvanometer,  a  distinct  and 
equal  swing  of  the  spot  to  the  right  and  to  the  left,  and  that  if 
sent  through  the  eyeball  is  fully  adequate  to  arouse  a  normal 
(positive)  blaze. 

I  now  send  a  break  shock  through  the  eyeball  (and  galvano- 
meter) in  the  positive  direction,  and  you  see  the  galvanometer 


lit.]  '  ELECTROCUTION  49 

spot  sharply  deflected  to  your  right.  "  Naturally,"  you  say, 
"  since  it  has  been  traversed  by  an  induction  shock  in  a  positive 
direction,  and  '  positive '  is  to  our  right."  But  notice  the  magni^ 
tude  of  the  deflection,  notice  also,  how  slowly  it  is  subsiding ; 
that  has  not  been  any  short  kick  by  an  induction  shock,  but 
something  more,  it  has  been  a  positive  kick  heralding  our  now 
familiar  friend,  the  positive  blaze.  And  you  will  be  quite  sure 
that  this  has  been  so,  when  you  see  the  effect  of  sending  a  break 
shock  through  the  eyeball  (and  galvanometer)  in  the  negative 
direction.  Now,  you  have  a  short,  sharp  kick  of  the  spot  to  the 
left  by  the  induction  shock,  and  a  prolonged  large  deflection  to 
the  right,  slowly  subsiding,  evidently  the  electrical  expression 
of  what  by  this  time  we  are  tempted  to  call  the  retinal  blaze 
(but  vide  infra  as  regards  the  justification  of  "  retinal "). 

§  29.  Electrocution. — The  proof  has  to  be  completed  by 
showing  that  these  blaze  effects  do  not  occur  on  a  dead  eye- 
ball. I  killed  the  last  eyeball  by  putting  it  into  hot  water,  I 
will  kill  *  this  one  by  electrocution,  a  method  that  has  the 
advantage  of  leaving  the  eyeball  undisturbed  between  the  elec- 
trodes, and  then  apply  the  test  of  an  induction  shock  right  and 
left  through  eyeball  and  galvanometer.  I  strengthen  the  cur- 
rent, sliding  the  secondary  quite  home  over  the  primary,  and 
tetanise  for  half  a  minute  or  so  with  these  strong  currents 
(taking  care,  of  course,  to  plug  out  the  galvanometer  to  preserve 
it  from  such  currents).  Finally,  1  unplug  the  galvanometer  and 
apply  the  double  test.  The  positive  break  shock  gives  a  sharp 
deflection  to  the  right,  the  negative  break  shock  gives  a  sharp 

*  It  has  been  objected  to  me  that  I  cannot  tell  whether  the  eyeball  has 
really  been  killed,  may  not  be  merely  shocked,  would  not  in  time  recover. 
In  point  of  fact  I  do  not  think  it  has  been  finally  killed,  but  the  discussion 
need  not  be  entered  upon  further,  our  sufficient  point  is,  that  blaze-currents 
are  not  manifested  by  an  electrocuted  eyeball,  and  it  does  not  matter  to  us 
whether  this  inert  state  is  that  of  death  or  of  shock.  A  similar  objection  has 
been  made  with  reference  to  capital  punishment  by  electrocution,  and  in  this 
case  accidental  recovery  is  guarded  against  by  a  prompt  "  post-mortem  "  ex- 
amination. For  the  conditions  of  recovery  or  non-recovery  of  electrocuted 
animals,  cf.  Prevost  and  Batelli,  Journal  de  Physiologie  et  de  Pathologie 
Gdndrale,  1899,  pp.  399,  427,  1085,  1128  ;  1900,  pp.  40,  422,  443,  755. 

D 


50 


TtlE  SIGNS  OF  LIFE 


[lect. 


and  equal  deflection  to  the  left.  There  is  no  blaze.  The  eye- 
ball is  dead,  or  in  that  state  of  latent  life,  or  temporary  non- 
living state  to  which  we  give  the  name  of  "  shock."     Evidently, 


10  m. 


40  m. 


&0 

Fig.  2  2. — Frog's  eyeball,  induction  coil  and  galvanometer  in  series.  Effects  of 
single  break  induction  shocks  in  positive  and  negative  directions  before  and  after 
"  electrocution  "  by  strong  tetanisation. 

as  regards  the  retina,  or  the  eyeball,  the  blaze  reaction  is  a 
very  nice  and  convenient  "sign  of  life." 

I  30.  The  three  types. — So  far,  the  several  experiments  that 
have  been  grouped  together  under  the  head  of  the  third  experi- 
ment (§  26),  have  come  off  perfectly  well,  and,  in  accordance, 
with  expectation  and  prediction. 

It  might  have  been  otherwise.  I  took  care  to  be  provided 
with  fresh,  normal,  uncompressed  eyeballs,  because  I  did  not 
wish,  in  introducing  the  subject,  to  have  to  confuse  your  first  im- 
pression of  it  by  interpolated  explanation  of  unexpected  results 
of  experiment.  And  I  was  careful  to  be  provided  with  the 
lively  Rana  Teniporaj'ia,  as  the  sluggish  R.  esculenta  would  pro- 
bably not  have  answered  as  well.  Nevertheless,  I  felt  it  neces- 
sary to  have  at  my  elbow  a  diagram,  in  which  are  schematically 
summarised  the  various  cases  that  I  have  met  with  in  various 
states  of  the  eyeball.     I  have  divided  them  into  three  types  : — 


m.] 


THREE  TYPES 


51 


(i)  Both  reactions  positive;  (2)  Both  reactions  homodrome  ; 
and  (3)  Both  reactions  negative ;  and  although  I  do  not  find  any 


Direction  of  exciting  current 


Negative 


Positive 


Type  I. 
The   response  to  excitation   in  both  direc- 
tions is  positive.      This  is  the  normal 
response. 


Type  II. 

The  response  to  excitation  in  the  negative 
direction  is  negative,  and  in  the  positive 
direction  positive. 


Type  III. 

The  response  to  excitation  in   both  direc- 
tions is  negative. 


Dead  Eyeball. 

The  response  to  negative  excitation  is 
positive  and  to  positive  excitation 
negative. 

Fig.  23. — Frog's  eyeball.     The  three  types  of  response  to  excitation  by  single 
induction  shocks  in  positive  and  negative  directions. 

strict  paralleHsm  between  these  three  types  of  electrical  response 
to  electrical  stimuli,  and  the  three  types  described  above  of 
electrical  response  to  luminous  stimuli,  I  do  find  correspondence 
to  this  extent  that  a  perfectly  normal  eye  gives  positive  response 
of  the  first  type  in  both  series,  while  a  considerably  compressed 
or  massaged  eye  gives  negative  response  of  the  third  type  in 
both  series.  The  extremes  in  the  two  series  correspond,  but  I 
fail  to  trace  correspondence  in  the  intermediate  and  transitional 
forms  of  the  two  series.  It  is  hardly  necessary  to  point  out  that 
the  very  existence  of  such  a  series  of  responses  graded  from 
positive  to  negative,  is  confirmatory  evidence  of  the  coexistence 
of  two  contrary  electro-motive  changes,  a  conclusion  which  we 
saw  reason  to  infer  from  the  effects  of  light  already  described. 


52  THE  SIGNS  OF  LIFE  [lect. 

§  31.  Cause  <  Effect. — I  have  thought  it  hardly  necessary  to 
repeat  to  you  a  series  of  experiments  similar  to  the  preceding, 
but  with  condenser  discharges  in  place  of  break  induction 
shocks.  Moreover,  time  forbids  that  I  should  do  so,  with  the 
explanation  necessary  to  bring  out  the  particular  advantages 
of  this  method.  We  may  find  time  for  this  at  a  future 
lecture,  meanwhile  I  will  again  refer  you  to  the  paper  already 
quoted,*  where  you  will  find  experimental  justification  for  the 
statement  that  the  electrical  energy  of  excitation  is  greatly 
exceeded  by  the  electrical  energy  of  the  blaze-current  that  it 
arouses. 

I  32.  Galvanisation.  Experiment  V. — The  fifth  and  last 
experiment  on  our  list  is  to  show  how  the  direction  of  a 
blaze  -  current  aroused  by  an  induction  shock,  can  be  modi- 
fied by  the  passage  of  a  galvanic  current  through  the  eye- 
ball. 

An  eyeball  is  put  up  as  before,  the  compensator  is  arranged 
to  give  a  current  of  comparatively  high  E.M.F.  (o.i  volt)  through 
the  eyeball  and  galvanometer,  I  first  take  this  galvanic  current 
in  the  positive  direction,  when,  of  course,  the  galvanometer  spot 
is  driven  off  scale  to  your  right.  I  bring  the  spot  back  in  scale 
by  means  of  a  controlling  magnet,  and  as  soon  as  it  is  steady, 
send  a  break  induction  shock  through  the  circuit  (comprising 
the  eyeball,  compensator,  and  galvanometer  in  series)  first  in  the 
positive,  then  in  the  negative  direction.  In  both  cases  the 
positive  deflections  are  greatly  augmented. 

Then  I  reverse  the  galvanic  current  to  the  negative  direction, 
readjust  the  spot  on  scale  by  means  of  the  controlling  magnet, 
and  repeat  the  test.  Both  the  induction  shocks,  positive  and 
negative  alike,  now  give  negative  deflections,  i.e..,  blaze-currents 
in  the  same  direction  as  the  galvanic  current.  Nothing  of  the 
sort  happens,  I  should  add,  in  the  case  of  a  dead  or  "  electrocuted  " 
eyeball.  If  I  had  made  the  experiments  upon  an  eyeball  giving 
negative  blaze-currents  of  the  third  type  described  above,  you 
would  have  witnessed  an  augmentation  of  these  currents  during 

*  Phil.  Trans.  Roy.  Soc,  vol.  194  B.,  p.  183.     1901. 


•] 


EXPERIMENT  V 


53 


negative  galvanisation,  and  their  reversal   to  positive  currents 
during  positive  galvanisation. 

I  think  these  points  will  be  best  illustrated  by  the  values 
obtained  in  some  previous  experiments  of  the  kind.  The  values 
are  approximate  only,  as  I  did  not  correct  for  kick  due  to  the 
induction  shock  itself 


Direction  of  Excitation 
by  Brealt  Shock  of  Berne 
Coil  at  1000  units,  with 
two  Leclauches  in  prim- 
ary circuit. 

Voltage  op  Response. 

During 

Galvanisation  by 

-  1/lOth  volt. 

Without 
Galvanisation. 

During 

Galvanisation  by 
+  a/10th  volt. 

+ 

-0.060 
-  0.040 

+  0.010 
+  0.010 

+  0.050 
+  0.030 

+ 

-0.024 
-0.033 

-0.019 
-0.029 

+  0.024 
+  0.019 

§  33.  Some  questions. — Our  experiments  are  at  an  end,  and 
so  is  the  lecturer's  hour.  But  I  will  tax  your  patience  for  five 
minutes  longer  and  attempt  to  answer  two  questions  that  must 
have  occurred  to  you  as  they  have  to  me.  How  much  of  this 
blaze-reaction  is  due  to  the  retina,  and  how  much  to  other 
tissues  of  the  eyeball  ?  Is  the  retinal  stuff  that  reacts  to  light 
the  same  'as,  or  different  from,  the  stuff  that  reacts  to  an 
induction  shock  ? 

I  cannot  fully  or  confidently  answer  either  of  these 
questions.  I  can  only  give  partial  and  tentative  answers,  and  I 
do  so  far  less  on  account  of  any  value  that  I  place  on  the  answers 
in  themselves,  than  because  I  believe  you  will  see  how  the  chief 
value  of  a  question — somewhere,  somehow — we  cannot  at  the 
outset  foresee  either  where  or  how — may  be  wrapped  up  in  our 
very  failure  to  obtain  a  neat  answer. 

At  first  I  thought  that  the  blaze-current  was  retinal,  like  the 
current  excited  by  light.  The  expression  "retinal  blaze" 
obtained  currency  in  the  laboratory,  and  the  title  of  my  first 
paper  runs,  "  On  retinal  currents  excited  by  light  and  excited 
electrically,"  and  the  title  of  my  second  paper  was  intended  to 
be  "  On  the  '  blaze-currents  '  of  the  Retina,"  but  it  soon  became 


54  THE  SIGNS  OF  LIFE  [lect. 

"  On  the  blaze-currents  of  the  Eyeball."  That  the  electrical 
response  of  the  eyeball  to  light  has  its  exclusive  seat  in  the 
retina,  is  proved  by  the  fact  that  of  the  two  halves  of  an  eyeball 
bisected  into  an  anterior  and  a  posterior  half,  only  the  latter 
responds  to  light,  and  if  further — as  recommended  by  Kiihne, 
the  retina  itself  be  separated  from  the  remaining  coats,  electrical 
response  to  light  persists  of  the  isolated  retina,  but  is  absent 
from  the  remaining  tissues.  But  a  similar  procedure  in  the  case 
of  electrical  response  to  electrical  excitation  taught  me  that  the 
reaction  is  not  confined  to  the  retina,  that  it  is  manifested  by 
the  anterior  as  well  as  by  the  posterior  half  of  the  eyeball,  that 
the  isolated  cornea  and  the  isolated  lens  give  blaze-currents.  I 
therefore  concluded  that  tissues  other  than  retinal  are  coeffective 
in  the  electrical  response  to  electrical  stimulation  of  the  entire 
eyeball,  and  accepted  the  fact  as  a  hint  to  examine  other  living 
tissues  for  this  presumably  common  sign  of  life.  Meanwhile, 
from  the  retinal  sheet  in  animals  excitable  by  light,  my  attention 
naturally  turned  to  the  chlorophyl  sheet  in  vegetables  presum- 
ably excitable  by  light,  and  a  demonstration  of  the  electrical 
response  to  light  in  green  leaves  was  the  immediate  result*  I 
tried  petals  of  flowers  in  the  same  way,  as  one  among  other 
control  tests  of  the  reality  of  the  leaf  response.  Petals  proved 
to  be  absolutely  inert  in  this  respect.  Yet  petals  are  obviously 
"  alive,"  so  I  tested  petals  by  the  blaze-test,  and  found  that  to 
this  test  petals  are  at  once  found  to  be  alive.  The  idea  by  this 
time  had  fully  generalised  itself  in  my  mind,  and  I  placed  all 
sorts  of  living  things,  animal  and  vegetable,  on  the  unpolarisable 
electrodes,  leaves,  stems,  seeds,  fruits,  etc.,  muscle,  nerve,  lung, 
liver,  pancreas,  skin,  hen's  eggs,  etc.,  and  found  that  some  things 
reacted  well,  and  others  not  at  all,  or  irregularly.  But  these 
were  digressions — digressions,  however,  that  have  in  my  opinion 
become  far  more  interesting  than  the  original  questions. 

§  34.  To  return  to  the  second  of  these.  To  get  an  indica- 
tion whether  the  same  or  two  different  substances  react  to 
light  and  to  induction  shocks,  I  looked  for  modifications  of  the 

*  Waller. — "  The   Electrical   Effect   of    Light  upon    Green    Leaves," 
rroc.  Roy.  Soc,  vol.  67,  p.  129,  1900, 


•] 


TETANISATION  AND  ILLUMINATION 


55 


response  to  light  by  strong  tetanisation,  and  vice  versa  for  modi- 
fications of  the  response  to  induction  shocks  by  strong  illumina- 
tion, I  also  took  series  of  positive  responses  to  light  and  to 
weak  tetanisation  alternated,  to  see  whether  or  no  they  would 
decline  pari  passu.      An  example  of  such  a  series  has  been 


Fig.  24. — Frog's  eyeball.  Series  of  normal  responses  to  light  and  to  tetanisation 
alternated  ;  each  excitation  lasts  for  one  minute.  The  response  to  tetanisation  falls 
more  rapidly  than  that  to  light. 

figured  above.  The  series  of  responses  to  tetanisation  appears 
to  decline  more  obviously  than  does  the  series  of  responses  to 
light.  But  the  difference  is  not  very  striking,  and  in  other 
records  it  is  even  less  so.  In  fact,  when  I  took  the  records,  I 
thought  they  justified  me  in  saying  that  the  two  kinds  of  response 
wear  out  in  a  parallel  manner.  Clearly,  however,  the  parallelism 
has  not  always  if  ever  been  absolute  ;  the  instance  figured  above 
exhibits  more  rapid  decline  of  the  tetanisation  responses  than 
of  the  light  responses.  The  point  clearly  needs  to  be  tested 
again.  As  regards  modification  of  the  response  to  induction 
shocks  by  strong  illumination,  we  have  seen  that  no  appreciable 
effect  occurs.  As  regards  modification  of  the  response  to  light 
by  strong  tetanisation,  we  have  seen  that  the  regular  effect  has 
been  an  increased  response  during  and  after  tetanisation.  Indeed, 
the  resistance  of  the  retina  as  regards  its  excitability  by  light 
has  been  a  constant  yet  surprising  feature.  The  strongest  tetani- 
sation at  my  disposal  (Berne  coil,  2  Leclanches,  secondary  over 
primary  coil,  current  unbearable  by  wetted  fingers)  has  failed 
to  abolish  its  response  to  light.  And  strong  tetanisation  (10,000 
units)  that  has  completely  abolished  all  blaze-reaction  (as  e.g.^ 


56  THE  SIGNS  OF  LIFE  [lect. 

in  the  experiment  of  Fig.  22)  has  left  the  response  to  light 
unaltered. 

On  review  of  all  these  facts,  I  am  inclined  to  think  that,  as 
regards  their  action  upon  the  retina,  the  two  forms  of  excita- 
tion act  upon  two  distinct  but  closely  related  substances  holding 
to  each  other  the  relation  of  pro-substance  and  substance,  the 
former  acted  upon  by  electrical  currents  and  not  by  light,  the 
latter  acted  upon  by  light  and  not  by  electrical  currents. 

Among  the  tissues  that  give  most  dubious  results  in  a  first 
rapid  survey  of  blaze-currents,  the  skin  was  one  of  the  most 
notable.  I  therefore  studied  it  the  more  closely.  The  next  two 
lectures  will  be  given  to  the  consideration  of  "  Skin-currents." 

I  35.  The  crystallme  lens. — Further  investigation  of  the  blaze- 
currents  manifested  by  the  anterior  parts  of  the  eyeball  led 
to  very  definite,  constant,  and,  I  may  add,  quite  unexpected, 
results.  The  observations  relating  to  this  matter  were  made  at 
the  sea  coast  during  the  months  of  August  and  September 
of  last  year — principally  on  the  crystalline  lens  of  freshly 
caught  fish— and  may  be  most  briefly  described  by  the  following 
quotation : — * 

"  In  the  course  of  investigation  of  the  effects  of  light  and  of 
electrical  excitation  on  the  frog's  eyeball,  I  came  to  the  con- 
clusion that  tissues  other  than  retinal  are  coeffective  in  the 
response  to  strong  induction  shocks,  and  proceeded  therefore 
to  look  for  blaze-currents  in  other  living  tissues. 

"  The  particular  point  that  aroused  my  attention  in  the  case 
of  the  eyeball  was  the  fact  that  the  anterior  half  of  the  eyeball 
was  sometimes  found  to  give  a  larger  response  than  the  posterior 
half,  and  the  present  observations  proceed  from  an  attempt  to 
determine  the  principally  effective  part  in  such  reaction.  And 
I  may  state  at  once,  as  my  chief  conclusion,  that  it  is  the 
crystalline  lens. 

"  The  eyes  upon  which  the  determination  was  made,  in  the 
first  instance,  were  those  of  fish — whiting  and  mackerel — by 
reason  of  the  fact  that  these  were  for  a  season  at  my  disposal 

*  "  On  the  Blaze-currents  of  the  Crystalline  Lens,"  Proc,  Roy.  Soc, 
4th  December  1902, 


!•] 


LENS  CURRENTS 


57 


quite  fresh  from  the  sea.  I  subsequently  made  similar  observa- 
tions on  the  eyes  of  octopus,  on  sheep's  eyes  fresh  from  the 
slaughter-house,  and  on  the  eyes  of  recently  killed  cats  and 
rabbits. 

"  The  point  that  was  most  striking  in  these  first  observations 
was  the  great  endurance  of  the  reaction  in  the  crystalline  lens 
as  compared  with  its  rapid  disappearance  from  the  remaining 
tissues  of  the  eyeball  and  from  the  skin,  and  with  the  rapid 
disappearance  of  the  direct  electrical  excitability  of  muscle.  I 
should,  as  an  outcome  of  these  observations,  look  for  the  last 
sign  of  life  of  a  fish  by  testing  the  crystalline  lens,  whereas  in 
the  case  of  man  I  should  test  a  piece  of  skin.  The  reaction — as 
far  as  I  have  yet  seen — has  been  completely  absent  from  frozen 
fish  (salmon)  as  received  from  London  fishmongers.  Its  normal 
direction  in  the  lens  is  '  negative,'  i.e.,  from  external  to  internal 
pole.  It  is  abolished  by  heat  (70°)  and  by  pressure.  A  typical 
pair  of  responses  is  illustrated  by  the  following  record  : — 


25  mins. 


Fig.  25. — Codfish.     Antidrome  and  homodrome  responses  of  the  isolated  lens, 
from  anterior  to  posterior  pole,  of  -0.0009  and  -0.0022  volt  respectively. 


58  THE  SIGNS  OF  LIFE  [lect.  in. 

"  I  conclude  from  this  and  similar  experiments — 

"  I.  That  a  crystalline  lens  of  suitable  size  is  a  good  object 
upon  which  to  study  the  nature  of  blaze-currents. 

"  2.  That  a  '  blaze-current '  is  a  physical  sign  of  the  '  living ' 
state. 

"  3.  That  a  blaze-current  may  be  post-kathodic  as  well  as 
post-anodic,  antidrome  as  well  as  homodrome. 

"4.  That  the  normal  direction  of  blaze-currents  in  the  crystal- 
line lens  is  negative  or  ingoing,  i.e.,  from  the  external  or  anterior 
to  the  internal  or  posterior  pole." 


REFERENCES 


Waller. — "  On  the  Retinal  Currents  of  the  Frog's  Eye,  excited  by  Light 

and  excited  Electrically,"   Proc.  Roy.  Soc,  Ixvi.,  p.  327  ;  Phil.  Tra?ts. 

Roy.  Soc,  B  vol.  193,  p.  123. 
Waller. — "The   Eyeball  as   an   Electrical  Organ,"   Proc.   Physiol.    Soc, 

loth  November  1900. 
Waller. — "On  the    'Blaze-currents'  of  the  Frog's  Eyeball,"   Proc.  Roy. 

Soc,  Ixvii.,  p.  440  ;  Phil.  Trans.  Roy.  Soc,  B  vol.  194,  p.  183. 
Waller. — "Le  Dernier  Signe  de  Vie,"  Comptes  Rendus  de  f  Academic  des 

Sciences,  3rd  September  1900. 
Waller. — "  On  the  Blaze-currents  of  the  Crystalline  Lens,"  Proc  Physiol. 

Soc,  November  1902  ;  Proc  Roy.   Soc,  4th    December  1902  ;  Engel- 

jnanrCs  Archiv  f.  Physiologic. 
DURIG. — "A  contribution  to  the  action  of  Blaze-currents," /"riJf.  Roy.  Soc, 

4th  December  1902. 


LECTURE  IV 

Skin-currents  (of  the  Fi-og) — The  Normal  Current  is  "Ingoing" — The  Re- 
sponse to  Indirect  Excitation  is  Outgoing,  Mixed,  or  Ingoing — The  Latent 
Period  is  Two  Seconds — Fatigue — Atropine — Mercuric  Chloride — The 
Response  to  Direct  Excitation  is  Outgoing — Summation — Effects  of 
Tetanisation — Localisation  of  the  Response  by  the  ABC  Method — 
Terminology. 

§  36.  From  the  preliminary  observations  alluded  to  in  my 
last  lecture  (§  33),  I  formulated  the  following  working  rule  for 
the  experimental  distinction  between  the  living  and  the  dead 
states  of  matter  : — 

"  If  the  object  of  examination  exhibits  blaze  in  one  or  in 
both  directions,  it  is  living."  * 

One  of  the  earliest  objects  of  examination  upon  which  I 
tested  this  rule  was  the  human  body,  living  and  dead.  I  thought 
that  it  might  be  possible  to  place,  e.g.,  a  finger  between  a  pair  of 
electrodes,  and  to  learn  from  the  presence  or  absence  of  blaze 
reaction  whether  the  finger  was  living  or  dead.  But  by  reason 
of  the  fact  that  a  finger  is  covered  by  skin,  and  that  it  is  im- 
possible to  send  current  by  unpolarisable  electrodes  into  the 
intact  human  body  otherwise  than  through  skin  (or  mucous 
membrane),  the  question  has  proved  to  be  much  less  simple  than 
it  appeared.  It  has  involved  me  in  an  investigation  of  skin- 
currents  that  has  taken  the  best  part  of  two  years,  and  the 
results,  instructive  though  they  are  as  regards  the  original 
question,  are,  I  think,  of  still  greater  interest  from  another  point 
of  view.  It  will  be  well,  therefore,  to  consider  ourselves  as 
entering  upon  a  fresh  field,  albeit  an  already  much  trodden  field, 
in  undertaking  an  exploration  of  "  Skin-Currents." 

*  I  do  not  commit  myself  to  the  obverse,  that  if  an  object  exhibits  no 

blaze  it  is  not  alive.     Vide  mfra,  §  82, 
59 


60 


THE  SIGNS  OF  LIFE 


[lect. 


We  shall  study  the  skin-currents  of  the  frog,  of  the  cat, 
and  of  man,  also  the  currents  of  mucous  membranes  and  the 
currents  of  vegetable  "  skins."  To-day  we  shall  confine  our- 
selves to  the  case  of  the  frog,  examining :  {a)  the  normal 
current,  {b)  the  effects  of  indirect  excitation,  {c)  the  effects  of 
direct  excitation. 


§  37.  The  normal  current. — A  piece  of  skin  of  the  back,  or 
indeed  of  any  part  of  the  body,  carefully  excised  and  placed 
between  unpolarisable  electrodes,  gives  current,  directed  from 
outer  to  inner  surface  (through  the  skin).  This  "  ingoing " 
"  negative "  or  centripetal  current  increases  during  observation. 
A  piece  of  skin  spread  upon  a  glass  plate  with  a  central  hole, 

and  placed  between  the  elec- 
trodes as  figured,  gives  current 
that  reflects  the  galvanometer 
spot  to  your  left.  And,  as  you 
notice,  the  spot  is  creeping 
further  to  the  left.  Two  re- 
flections arise  from  this  obser- 
vation :  clearly  the  current 
cannot  be  due  to  injury  of  the 
internal  surface,  since  in  that 
case  it  would  be  outgoing ; 
probably  the  increasing  nega- 
tive current  is  due  to  the  sub- 
sidence of  what  in  the  case  of 
the  eyeball  we  referred  to  as 
the  manipulation  blaze.  It 
looks  as  if  resting  skin  were 
the  seat  of  an  ingoing  current 
of  rest,  and  as  if  the  increasing 
negative  deflection  occurring  on  the  galvanometer  scale  were  in 
reality  a  decreasing  positive  effect  caused  by  the  previous 
disturbance  by  manipulation.  We  shall  find  confirmation  of  this 
view  later  on,  when  we  have  learned  that  direct  mechanical  and 
electrical  excitation  of  the  skin  gives  almost  invariably  a  positive 
or  outgoing  electrical  effect. 


Fig.  26. — Frog's  skin  on  a  perforated 
glass  or  ebonite  plate,  between  unpolar- 
isable electrodes.  The  external  surface 
of  the  skin  is  uppermost.  The  arrows 
signify  the  direction  of  "  normal  cur- 
rent "  —  "  ingoing,"  from  external  to 
internal  surface. 


IV.]  SKIN  CURRENTS  61 

§  38.  Indirect  excitation. — The  effects  on  the  skin  of  excita- 
tion of  its  nerves  are  particularly  interesting ;  it  is  easy  to 
demonstrate  them,  but  by  no  means  easy  to  interpret  them  in 
detail.  I  do  not  think  that  any  interpretation  yet  offered  has 
properly  embraced  all  the  facts,  and  I  shall  not  pretend  to  mend 
matters  much  in  this  respect.  But  I  will  lay  the  facts  before  you, 
more  completely  and  more  briefly  than  you  will  find  them  hitherto 
described,  by  means  of  graphic  records  that  exhibit  better  than 
any  narrative  the  character  and  dimensions  of  the  phenomena. 

The  experiment  I  am  about  to  show  you  is  one  that  was 
first  made  by  Roeber  (on  the  suggestion  of  Rosenthal)  more 
than  thirty  years  ago,  and  that  has  since  been  repeated  with  varia- 
tions by  Engelmann  and  by  Hermann.  The  preparation  is  as 
follows  : — A  frog's  sciatic  nerve  is  dissected  out  in  the  usual  way, 
the  foot  is  cut  off,  the  skin  of  the  leg  is  longitudinally  divided  on 
the  anterior  aspect  and  peeled  off  the  leg  up  to  the  knee-joint, 
the  leg  is  cut  off  just  below  the  knee-joint,  the  femur  and  thigh 
muscles  are  divided  just  above  the  joint.  We  now  have  a  sciatic 
nerve  in  connection  with  the  skin  of  the  leg,  and  the  ends  of  the 
femur  and  tibia  serving  as  a  handle.  The  skin  is  now  laid  over 
one  leading-off  electrode,  and  the  other  electrode  is  brought  into 
contact  with  the  other  surface  of  the  skin,  the  sciatic  nerve  is 
laid  across  a  pair  of  exciting  electrodes  that  are  connected  to  a 
coil.  We  now  have  a  nerve-skin  preparation,  the  analogue  of  a 
nerve-muscle  preparation,  quite  as  easy  to  make,  and  affording, 
when  made,  an  unfailing  demonstration  of  a  current  of  animal 
electricity  and  of  the  action  of  nerve  on  skin.  It  ought  long  ago 
to  have  become  a  regular  lecture  experiment  and  student's 
exercise,  yet  somehow  or  other  it  has  almost  dropped  out  of 
notice.  Every  student  of  physiology  makes  nerve-muscle  pre- 
parations by  the  score.  I  wonder  how  many  students  or  teachers 
have  ever  made  a  nerve-skin  preparation,  and  what  would  be 
said  if,  as  a  change  from  the  regular  round  of  about  six  practical 
experiments  (that  cannot  be  properly  done  in  the  time  allowed) 
an  examiner  were  to  ask  an  honours  candidate  to  show  some- 
thing by  means  of  a  nerve-skin  preparation. 

Well,  our  experiment  is  waiting,  and  the  spot  has  come  to 
rest.     The  normal  skin  current  is  ingoing  and  increasing,  the 


62  THE  SIGNS  OF  LIFE  [lect. 

spot  has  crept  to  the  left  of  the  scale,  therefore  to  the  left  signi- 
fies ingoing,  to  the  right  outgoing ;  but  we  shall  verify  this 
presently  with  a  bit  of  zinc. 

I  tetanise  the  nerve  for  a  second  or  two,  and  after  a  distinct 
interval,  long  enough  to  allow  the  thought  that  there  is  no 
effect,  the  spot  sweeps  across  the  scale  to  the  right,  signifying 
that  the  skin,  aroused  by  excitation  of  the  sciatic  nerve,  has  given 
an  outgoing  current.  And  knowing  what  to  expect,  I  took  care 
to  shunt  the  galvanometer,  for  the  resistance  of  the  skin  is  so 
low,  and  the  voltage  of  response  so  great,  that  the  spot  would 
assuredly  have  flown  off  scale  if  the  galvanometer  had  not  been 
shunted.  I  wanted,  however,  to  have  a  measurable  effect,  such 
as  should  allow  us  to  make  further  trials.  Five  minutes  have 
elapsed,  and  I  repeat  the  excitation  ;  deflection  to  the  right  occurs 
again,  but  is  much  smaller.  It  looks  as  if  the  nerve-skin  pre- 
paration were  becoming  fatigued.  And  while  we  wait  for  a 
second  five  minutes  to  elapse,  let  us  consider  matters.  How 
has  the  nerve  acted  upon  the  skin  ?  What  is  the  meaning  of 
the  declining  effect  we  are  looking  for  ?  Is  the  response  always 
in  this  positive  or  outgoing  direction  ? 

All  authorities  who  have  worked  at  the  subject  are  agreed 
that  it  is  upon  the  skin-glands  that  the  nerve  acts,  and  that  the 
skin  effect  is  the  sign  of  a  glandulo-motor  or  secreto-motor 
phenomenon.  I  share  this  view,  and  do  not  think  it  probable 
that  nerve  has  any  connection  with  the  general  epithelial  invest- 
ment of  the  skin  ;  but,  in  remembrance  of  the  fact  that  cutaneous 
pigment  cells  are  demonstrably  influenced  through  nerves,  I 
make  some  mental  reservation  to  the  assumption  that  the  effect 
is  exclusively  glandular.  The  wearing-out  of  the  response  in 
repetition  is  not  due  to  wearing-out  of  the  nerve,  nor  even 
wholly,  I  think,  to  wearing-out  of  the  discharging  gland,  but 
more  probably  to  a  wearing-out  of  the  junction  between  nerve- 
fibre  and  gland-cell. 

The  second  five  minutes  is  at  an  end,  and  now  you  see  that 
excitation  gives  a  negative  instead  of  a  positive  response,  and 
thus  answers  the  last  of  the  three  questions  we  put  a  few 
minutes  ago.  Clearly,  the  response  is  not  always  positive  or 
outgoing ;    you   have  just   seen    that   it    may   be    negative   or 


IV.] 


THREE  TYPES  OF  RESPONSE 


63 


ingoing,  and  I  may  add,  to  complete  the  account,  that  it  may 
also  be  "mixed" — negative  then  positive,  or  positive  then  nega- 
tive, or  positive  negative  positive.* 

And  now  that  you  have  witnessed  a  representative  experi- 
ment, I  will  project  on  the  screen  the  records  of  some  previous 
experiments. 


voLt 
ooi 


becand. 


Fig.  27. — Frog.     Nerve-skin  response. 
(i)  Positive  or  outgoing.         (2)  Mixed.         (3)  Negative  or  ingoing. 

§  39.  Latent  period. — Here  are  a  couple  of  photographic 
records,  taken  on  a  more  rapidly  travelling  plate,  in  order  to 
bring  out  more  distinctly  what  was  already  obvious  to  simple 

*  The  accounts  given  by  previous  observers — by  Engelmann  and  by 
Hermann  in  particular — are  not  quite  easy  to  reconcile  -with  each  other,  and 
with  the  description  given  in  the  text  of  these  lectures.  Thus  Engelmann,  in 
1872,  concluded  that  the  usual  effect  of  indirect  excitation  is  a  "  negative  varia- 
tion" of  the  normal  (ingoing)  current  Hermann,  in  1878,  gives  the  usual 
and  principal  effect  as  being  a  "positive  variation"  of  the  normal  current. 

The  two  accounts  are  summarised  in  the  following  diagram,  and  their 


64 


THE  SIGNS  OF  LIFE 


[lecT. 


inspection — viz.,  the  great  delay  between  excitation  and  response 
— about   two   seconds   with   a   fresh   preparation,   about   three 


VoU. 

■00£}- 
■004- 
■003- 
■002.- 
•001  - 


I       I I I L 


r      I I 1 I      1      I 1 I I 1 1 — 1 : — L. 


10 


30  seed. 


VoU. 
■ooz- 


001  - 

^y^ 

— 

,   ,   , 

c 

5 

10 

zo 

30  sec 

Fig.  28. — Frog.  Nerve-skin  preparation.  Galvanometric  records  of  the  lost 
time  of  the  response  to  indirect  excitation  by  tetanisation  of  the  sciatic  nerve.  Lost 
time  =  2  to  3  sees.     Lost  time  of  the  galvanometer  itself  =  \  sec. 


relation  to  that  given  in  the  text  vi^ill  be  easily  traced  if  it  be  remembered 
that  there  all  outgoing  effects  read  upwards  and  all  ingoing  effects  down- 
wards. 


r     "UsudL" 

.IJngclrnannl  ,^  ^, 

L  "Eccceptiona  L ' 


Hermann. 


("EoocepbionaL" 


1    . 


VsuaL" 


OuCgoing 


Ingoing 


Fig.  29. 


IV.]  ATROPHINE  ;  MERCURIC  CHLORIDE  65 

seconds  as  the  response  becomes  more  sluggish.  And  this 
has  been  a  true  physiological  latency  ;  it  is  of  the  same  order 
as  the  similar  effect  that  will  be  demonstrated  to  you  on  a 
mammal,  which  a  priori  you  might  have  expected  to  react 
more  quickly  {infra,  p.  105).  With  the  capillary  electrometer, 
and  excitation  by  a  single  strong  induction  shock,  the  latency 
came  out  at  0.9  sec. 

§  40.  In  connection  with  the  action  of  nerve  upon  skin,  one 
naturally  thinks  of  atropin — the  drug  which  so  promptly  abolishes 
the  action  of  secreto-motor  nerve — and  remembering  how  small 
a  dose  of  atropin  dries  the  mouth  and  dries  the  skin  in  the  case 
of  man,  you  have  reason  to  anticipate  that  atropin,  if  it  produces 
an  effect  at  all,  will  do  so  when  it  has  been  administered  to  the 
animal  by  subcutaneous  injection.  I  have  not  found  this  to  be 
the  case  in  two  experiments  ;  the  nerves  of  atropinised  frogs  acted 
perfectly  well  upon  the  skin,  but  after  the  drug  had  been  applied 
to  the  skin  itself,  the  nerves  ceased  to  be  effective.  So,  in  order 
to  demonstrate  that  atropin  acts,  it  will  be  preferable  to  test  it  by 
local  application  ;  and  to  show  this  quickly,  it  will  be  best  to  apply 
the  drug  to  the  external  surface  of  the  skin. 

A  second  nerve-skin  preparation  is  set  up,  for  an  experiment 
to  consist  of  three  steps.  These  will  be  :  firstly,  to  see  that  indirect 
excitation  (from  the  nerve)  is  effective  ;  secondly,  to  apply  atropin 
to  the  skin,  and  see  that  the  indirect  effect  is  abolished,  but  that 
an  effect  can  still  be  produced  by  direct  excitation  ;  finally,  to 
show  that  this  direct  effect  is  abolished  by  mercuric  chloride. 

With  indirect  excitation  you  see  that  the  large  deflection  before 
application  of  atropin  has  been  completely  abolished  by  atropin. 
The  nerve  no  longer  acts  upon  the  skin.  But  the  response  to 
direct  excitation  is  quite  well  marked ;  (and  note  in  passing  that 
it  is  to  your  right — in  the  positive  or  outgoing  direction).  I  now 
apply  some  mercuric  chloride  solution  to  the  external  surface,  and 
you  see  that  direct  excitation  gives  no  response.   The  skin  is  dead. 

§  41.  The  effects  of  direct  excitation  deserve  and  will  repay 
closer  study.  The  first  and.  only  allusion  to  these  effects  that  I 
am  acquainted  with,  occurs  in  Engelmann's  paper  of  1872,  sub- 

E 


66  Th£  signs  of  life  [lect. 

sequent  observers  having  principally  studied  the  effects  of  direct 
excitation  on  the  mucous  membranes  (Biedermann),  and  on  the 
skin  of  the  eel  (Reid).  Engelmann  seems  to  have  obtained  a 
negative  variation  of  the  current  of  rest — i.e.,  presumably  an  out- 
going effect — but  he  took  no  account  of  direction  of  excitation. 
Biedermann,  in  the  mucous  membranes  of  the  tongue  and  of  the 
stomach,  observed  positive  and  negative  variations  of  the  current 
of  rest ;  but  in  the  case  of  the  tongue  two  layers  of  mucosa  are 
under  experiment,  and  in  any  case  a  mucosa  is  not  the  same 
thing  as  the  skin. 

Reid  found  that  direct  excitation  of  the  eel's  skin  by  induc- 
tion shocks  of  either  direction  caused  ingoing  effects,  sometimes 
preceded  by  outgoing  effects.  I  have  made  a  large  number  of 
experiments  on  this  point  with  the  same  disposition  of  apparatus 
as  that  described  in  a  previous  lecture  in  the  case  of  the  eyeball, 
with  results  that  have  practically  been  invariable,  i.e..,  with  only 
one  or  two  exceptions  in  several  hundred  experiments.  So  that 
I  am  practically  certain  that  in  the  experiment  you  are  about  to 
witness,  direct  excitation  of  the  frog's  skin  by  an  outgoing  or  by 
an  ingoing  induction  shock  will  cause  an  outgoing  skin  response. 

\Expejdmenti\ 
A  piece  of  skin  is  set  up  between  unpolarisable  electrodes, 
as  in  Fig.  26,  and  connected  with  a  keyboard,  galvanometer, 
coil,  and  compensator,  as  in  Fig.  19.  We  are,  in  fact,  about  to 
test  the  skin  for  blaze-currents,  just  as  we  previously  tested  an 
eyeball  or  a  seed.  Compensation  is  established  (the  galvano- 
meter is  shunted  because  a  large  effect  is  expected).  With 
the  galvanometer  plugged  out  of  circuit,  a  break  induction 
shock  is  sent  through  the  skin  in  the  positive  (outgoing) 
direction  (spot  to  your  right),  and  immediately  afterwards  the 
galvanometer  plug  is  removed.  A  large  deflection  to  your 
right  occurs  ;  and  to  show  you  what  this  large  deflection  with 
the  shunted  galvanometer  means  as  regards  electro-motive 
force  of  the  excited  skin,  I  will  send  current  through  the  circuit 
from  -j^  of  a  volt ;  the  skin  response  has  been  two  or  three 
times  as  great,  i.e.,  its  voltage  has  been  0.02  to  0.03  ;  and  this 
is  by  no  means  a  maximum  value,  I  have  seen  it  as  much  as 


•] 


DIRECT  EFFECTS 


67 


o.io  volt.  The  positive  response  is  declining,  rapidly  at  first, 
then  more  slowly,  and  as  soon  as  the  spot  is  fairly  steady,  I 
compensate  and  repeat  the  excitation  in  the  reverse  (ingoing) 
direction,  and,  as  before,  you  witness  a  large  positive  (outgoing) 


voLb 


30  mins. 


Fig.  30. — Frog's  skin.  Response  to  direct  electrical  excitation.  The  first 
deflection  is  by  a  standard  voltage.  The  next  two  small  deflections  are  in  response 
to  +  and  -  break  induced  shocks  with  the  coil  at  1000  units.  The  last  two  large 
deflections  are  with  the  coil  at  5000.  (The  principal  "outgoing"  effect  is  preceded 
by  a  brief  ingoing  effect  in  the  case  of  ingoing  excitation.) 

deflection,  which,  although  in  the  direction  of  a  polarisation 
counter-current,  is  a  blaze-current,  like  the  antidrome  blaze- 
current  of  the  eyeball  (p.  47).  Indeed,  these  skin  effects  are 
precisely  similar  to  the  effects  you  have  already  seen  in  the 
case  of  the  eyeball.  The  positive  response  to  positive  excita- 
tion is  the  unequivocal  blaze,  the  positive  response  to  negative 
excitation  is  the  equivocal  blaze. 

And  to  complete  the  proof,  I  will  kill  the  skin  either  with 
a  few  drops  of  mercuric  chloride  solution,  or  by  plunging  it 
into  hot  water,  and  now  the  skin  gives  no  response  at  all 
to  either  direction  of  excitation.  The  spot  does  not  stir.  If  I 
unshunted  the  galvanometer  we  might  see  the  small  polarisa- 
tion effects  that  occur  with  any  electrolyte.  But  this  is  an 
unessential  point,  and  we  will  leave  the  galvanometer  as  it  is 


68 


THE  SIGNS  OF  LIFE 


[i 


for  our  further  experiments,   i.e.,  with  its   scale  to  take  in  a 
range  of  about  0.05  volt. 

§  42.  Summation. — The  positive  response  of  the  skin  is  ordi- 
narily of  considerable  duration  ;  in  general,  the  stronger  the 
stimulus,  the  longer  the  response  ;  five  minutes  has  been  a  very 
ordinary  duration  in  these  experiments.  If,  then,  a  second 
stimulus  is  applied  at  the  end  of  one  or  two  minutes,  before 
the  first  response  has  fully  subsided,  we  shall  obtain  a  second 
response  superposed  on  the  first,  and  so  on  for  a  third  and 
fourth  and  n*^  response,  which  give  a  summation  of  effects  by 
successive  deflection  remainders.  Here  is  a  record  that  will 
make  this  point  clear. 


vobt 


30  mins. 


Fig.  31. — Frog's  skin.  Summating  effect  of  excitation  at  intervals  of  2  mins. 
(The  first  response  is  to  a  weaker  excitation.) 

With  stimuli  at  shorter  intervals,  the  summation  is  steeper, 
and  the  individual  effects  of  which  it  is  composed  may  be 
indistinguishable.  There  is  a  fusion  of  deflections  analogous 
with  the  tetanic  fusion  of  muscular  contractions  with  which  we 
are  all  familiar. 

By  reason  of  this  summation,  and  of  the  fact  that  both 
directions  of  induction  shock  arouse  response  in  one  and 
the  same  (positive)  direction,  the  rapidly  alternating  currents 
of  an  induction  coil  as  ordinarily  used  for  tetanisation  give 
rise  to  a  much  larger  (positive)  response  than  does  a  single 


IV.] 


ABC 


69 


shock  at  the  same  strength  of  coil.  This  is  a  summation  of 
effects.  Moreover,  if  a  strength  of  coil  be  taken  so  small  as 
to  produce  no  response  with  single  shocks,  tetanisation  at  the 
same  strength  will  bring  out  an  evident  or  even  large  positive 
response.  Notice  that,  in  making  this  experiment  with  tetanisa- 
tion, I  have  taken  the  response  immediately  after  and  not 
during  tetanisation.  A  similar  effect  can  be  brought  out  during 
tetanisation,  and  in  cases  (like  the  present)  where  there  is  a 
clear  and  manifest  effect  in  one  direction,  we  may  without 
fear  of  fallacy  demonstrate  that  effect  during  as  well  as  after 
tetanisation.  But  in  doubtful  cases  (p.  131)  there  is  con- 
siderable difficulty  in  distinguishing  a  true  blaze-current  from 
the  disturbance  of  the  galvanometer  by  the  necessarily  strong 
currents  used,  and  from  the  relatively  large  polarisation  currents 
manifested  during  strong  tetanisation.  For  this  reason  I  have 
deliberately  abstained  from  laying  any  stress  upon  the  effects 
produced  during  tetanisation,  and  have  limited  myself  to  the 
information  obtainable  with  and  after  single  shocks,  and  after 
tetanisation. 


§  43.  The  ABC  plan. — With  a  piece  of  skin  arranged  as 
shown  in  Fig.  32,  an  induction  current  passed  through  the 
skin  in  the  positive  direc- 
tion from  B  to  A  has  its 
anode  at  the  lower  surface 
B  and  its  kathode  at  the 
upper  surface  A.  A  blaze- 
current  is  aroused  in  that 
same  direction  from  B  to 
A,  and  we  put  to  ourselves 
the  question  whether  that 
current  depends  upon  an  electro-positive  state  at  B,  or  upon  an 
electro-negative  state  at  A,  or  upon  both  states.  Or  more 
familiarly  put :  is  the  B  to  A  current  by  push  of  B,  or  by  pull 
of  A,  or  by  both? 

The  question  will  be  answered  by  the  following  plan  of 
experiment,  which  will  enable  us  to  examine  separately  the  two 
surfaces  B  and  A  by  connecting  first  one,  then  the  other,  with  an 


Fig.  32. 


70  THE  SIGNS  OF  LIFE  [lect. 

indifferent  point  C  through  the  galvanometer.  And  having 
done  this  by  a  first  pair  of  trials  with  excitation  from  B  to  A, 
we  shall  complete  the  experiment  by  a  second  pair  of  trials 
with  excitation  in  the  opposite  direction  from  A  to  B,  i.e.,  A 
having  been  anodic,  and  B  having  been  kathodic,  and  the 
blaze-current  being  as  before  in  the  outgoing  direction  from 
B  to  A. 

Try  to  forecast  the  result  a  priori,  as  I  did  ;  I  think  you  will 
probably  guess  wrong,  as  I  did.  I  imagined  at  this  stage  that 
we  had  to  do  with  something  of  the  nature  of  so-called  positive 
polarisation,  which  Hermann  and  Hering  have  shown  to  be  in 
reality  (in  the  cases  of  nerve  and  muscle)  post-anodic  action 
current.  On  this  view,  the  positive  effect  in  the  first  case  was 
presumably  due  to  a  post-anodic  "  push  "  at  B,  and  we  should 
therefore  expect  current  through  the  galvanometer  from  C  to  B 
(in  the  skin  from  B  to  C).  But  the  positive  effect  in  the  second 
case  could  not  be  explained,  post-anodic  "  push "  should  be  in 
the  negative  direction,  and  the  effect  observed  was  evidently 
either  by  post-anodic  "pull"  or  by  post-kathodic  "push" 
(through  the  skin). 

So  I  gave  up  forecasting  and  proceeded  to  experiments,  of 
which  I  hope  you  now  see  the  interest. 

We  shall  begin  by  a  first  pair  of  trials  to  localise  the  seat  of 
electro-motive  change  in  the  case  of  the  unequivocal  blaze- 
current,  positive  response  to  positive  shock.  We  shall  examine 
the  anodic  surface  B.  Therefore,  we  have  to  compensate  B  with 
C  (the  indifferent  point)  through  the  galvanometer,  then  to  send 
an  induction  shock  through  B  A,  then  to  reconnect  B  C  with  the 
galvanometer  to  observe  the  altered  electrical  state  of  B.  All 
which  we  have  now  done,  and  find  somewhat  to  our  surprise  that 
the  spot  does  not  stir,  i.e.,  that  the  electrical  state  at  B  has  not 
been  altered.  You  suspect,  perhaps,  as  I  did,  that  there  is  a 
break  in  the  galvanometer  circuit,  so  I  throw  a  ytjVtj  volt  into 
circuit,  and  you  see  by  the  movement  of  the  spot  that  the  circuit 
is  all  right. 

We  next  examine  the  kathodic  surface  A,  so  I  balance  A 
with  C  (the  indifferent  point)  through  the  galvanometer,  send 
then  an  induction  shock  through  B  A,  and  finally  reconnect  A  C 


.v.] 


ABC 


71 


with  the  galvanometer.  There  is  a  large  deflection  to  your 
right,  indicating  current  in  the  skin  from  C  to  A,  i.e.,  that  A  has 
been  rendered  electro-negative  to  C,  an  unaltered  point,  and  to 
other  unaltered  points  inclusive  of  B,  which  by  the  previous 
trial  you  saw  to  be  unaltered.  We  infer  from  this  first  pair  of 
trials  that  the  outgoing  (unequivocal)  blaze  B  A  depends  upon 
post-kathodic  "  pull "  under  A  at  or  near  the  outer  surface. 

Now  reverse  the  direction  of  excitation,  passing  the  induction 
shock  through  the  skin  in  the  negative  direction  from  A 
to  B. 

First  test  the  altered  state  of  B,  in  the  same  way  as  before 
(balance  B  with  C,  excite  through  A  B,  connect  B  C  with  the 
galvanometer),  there  is  no  effect.  Then  test  the  altered  state  of 
A  (balance  A  C,  excite  A  B,  connect  A  C),  there  is  a  large  deflec- 
tion to  your  right,  i.e.,  current  in  the  skin  from  C  to  A,  i.e.,  A  is 
electro-negative  to  unaltered  points  C  and  B,  etc.  We  infer 
from  this  second  pair  of  trials,  that  the  outgoing  (equivocal) 
blaze  B  A  depends  upon  post-anodic  "  pull "  under  A  at  or  near 
the  external  surface.  And  from  both  pairs  of  trials  we  infer  the 
simple  conclusion  that  the  blaze-currents  B  A — unequivocal  by 
excitation  B  A  and  equivocal  by  excitation  A  B — depend  upon 
an  electro-motive  action  aroused  at  or  near  the  external  surface. 
We  must  further  infer,  against  all  our  preconceptions  of  the 
matter,  that  this  electro-motive  action  is  aroused  by  the  kathode 
as  well  as  by  the  anode  of  an  exciting  current  {i.e.,  is  post- 
kathodic  as  well  as  post-anodic)  and  that  in  both  cases  it 
consists  in  an  electro-negative  state  of  the  active  part,  i.e.,  that 
this  part  is  galvanometri- 
cally  positive  to  inactive 
parts — the  seat  of  an  in- 
creased anionic  solution- 
pressure. 


Fig.  33. 


§  44.  Intact  external 
surface. — We  shall  find  in 
this  ABC  plan  a  ready  means  of  testing  an  intact  external 
surface,  and  of  thereby  learning  what  are  the  separate  contri- 
butions of  A  and  of  B  in  any  total  reaction  between  A  and  B  ; 


72  THE  SIGNS  OF  LIFE  [lect. 

we  shall  do  so  by  observing  the  separate  partial  reactions  A  C 
and  B  C.  Both  these  reactions  will  be  found  to  be  outgoing  at 
A  and  at  B,  being  directed  (in  the  skin)  from  C  to  A  and  from 
C  to  B. 

§  45,  There  has  been  one  very  striking  feature  in  the  fore- 
going experiments  that  must  at  once  have  attracted  your 
attention,  namely,  the  surprisingly  strict  and  limited  localisation 
of  the  reaction.  With  a  layer  of  skin  only  a  fraction  of  a 
millimetre  thick  between  our  exciting  electrode  A  and  B,  we 
saw  a  great  reaction  when  the  external  electrode  A  and  an 
indifferent  electrode  C  were  connected  with  the  galvanometer, 
but  no  reaction  at  all  when  the  connection  was  with  B  and  C  ; 
yet  in  this  case  also  we  had  quite  close  above  B  an  active 
area  A  that  might  have  been  expected  to  alter  the  potential 
of  B. 

J.  S.  MacDonald,  to  whom  I  had  the  pleasure  of  showing 
this  experiment,  said,  "  Oh,  there  must  be  a  membrane."  I 
think  he  is  quite  right,  but  I  am  unable  to  analyse  the  mode  of 
action  of  this  membrane. 

This  strictly  local  character  of  the  response— which  in  the 
present  case  of  electrodes  A  and  B  in  close  juxtaposition  is  as 
difficult  to  understand  as  it  is  easy  to  demonstrate — is  a  singularly 
favourable  condition  as  regards  the  experimental  application  of 
the  blaze  test  to  skin  and  to  other  animal  and  vegetable  tissues, 
in  which  there  is  little  or  no  diffusion  of  the  local  polar  effect 
of  excitation.  In  the  cases  of  muscle  and  of  nerve  these  local 
effects  are  to  some  extent  masked  by  the  propagated  distal 
effects  of  excitation,  and  require  for  their  manifestation  current 
strengths  greatly  in  excess  of  those  sufficient  to  give  maximal 
propagated  effects.  In  a  piece  of  skin,  or  in  a  leaf  or  petal — 
provided  they  are  alive,  the  excited  and  therefore  blazing  spot  is 
limited  as  to  depth  and  breadth,  and  the  exhaustion  of  that  spot 
by  excessive  stimulation  does  not  sensibly  modify  the  vitality  of 
parts  in  its  close  proximity.  Of  course  the  result  is  a  question 
of  degree  ;  the  entire  interpolar  length  of  a  tender  shoot  traversed 
longitudinally  by  violent  currents  is  stunned  (or  killed)  and  may 
shrivel  up  and  be  obviously  dead  in  a  day  or  two ;  a  flat  leaf 


IV. j  -      WHY  "BLAZE-CURRENTS?"  73 

traversed  by  violent  currents  will  exhibit  changes  outside  the 
polar  area  in  general  accordance  with  ordinary  current-diffusion. 
But  for  all  moderate  strengths  the  blaze  reaction  of  a  living  skin 
or  of  a  living  leaf  is  strictly  local. 

These  experiments  have  been  troublesome  to  follow,  as  they 
have  been  troublesome  to  demonstrate,  and  we  may  perhaps  find 
it  a  relief  from  a  somewhat  absorbing  effort  of  attention,  to  turn 
to  an  academic  discussion,  touching  the  nomenclature  of  these 
phenomena,  and  their  relation  to  other  known  phenomena,  and 
their  conceivable  biological  significance. 

§  46.  I  have  been  asked  why  I  chose  to  designate  the  effects 
by  the  name  of  "  blaze-currents  "  rather  than  "  positive  polarisa- 
tion currents,"  or  "  post-anodic  action  currents."  I  think  you 
will  readily  understand  the  answer  to  the  negative  parts  of  this 
question.  Apart  from  the  fact  that  the  name  "  positive  polarisa- 
tion," as  first  used  by  du  Bois-Reymond  to  designate  certain  homo- 
drome  effects  observed  by  him  in  muscle,  nerve,  and  electrical 
organs,  has  been  adversely  criticised  by  Hermann  and  Hering — 
shown  by  them,  indeed,  to  be  a  misnomer  inasmuch  as  the 
effects  to  which  it  was  applied  are  demonstrably  due  to  post- 
anodic  action  current — I  think  it  is  sufficient  to  refer  to  the 
equivocal  or  antidrome  blaze  as  forbidding  the  use  of  the  term 
"  positive  polarisation."  The  use  of  the  term  "  post-anodic 
action  currents"  you  have  just  seen  to  be  altogether  unjustified 
for  these  skin-currents  ;  in  one  case  the  current  is  not  post-anodic 
at  all,  and  in  the  other  it  is  post-anodic,  but  of  opposite  elec- 
trical sign  to  that  of  a  post-anodic  state.  In  muscle  and  in  nerve 
a  post-anodic  spot  is  galvanometrically  negative ;  in  the  skin  it 
is  galvanometrically  positive.  So  that  both  these  cumbersome 
expressions  are  happily  inapplicable,  and  a  new  term  is  required. 
I  have  been  led  to  adopt  the  term  blaze-current,  and  I  think 
you  may  now  understand  how  it  arose  in  the  study  of  retinal 
effects,  and  how  it  serves  to  clearly  earmark  a  natural  group  of 
phenomena  of  very  definite  physiological  meaning. 

A  blaze-current  is  literally  and  strictly  a  "current  of  action  "  ; 
but  it  is  a  particular  kind  of  action  current,  and  requires  a  dis- 
tinctive name.     The  known  phenomenon  to  which  it  bears  most 


74  THE  SIGNS  OF  LIFE  [lect. 

resemblance  is  the  discharge  of  an  electrical  organ,  and  we  shall 
not  infrequently  find  the  term  "  discharge  "  a  convenient  indica- 
tive word.  But  as  a  distinctive  and  specific  name,  the  word 
"  discharge  "  is  insufficient,  all  the  more  so  from  the  inconvenience 
that  would  arise  when  we  have  to  refer  to  the  blaze-currents 
aroused  by  the  condenser  discharge. 

I  have  had  another  reason  in  my  mind  that  has  helped  to 
make  me  use  the  expression  blaze-current.  The  great  mass  of 
living  things,  whatever  else  they  may  give  and  take  from  their 
surroundings,  take  oxygen  and  give  carbonic  acid  ;  they  may  live 
slowly  or  they  may  live  quickly — sluggishly  smoulder  or  suddenly 
blaze.  A  muscle  at  rest  is  smouldering,  a  muscle  in  its  contrac- 
tion is  blazing  ;  the  consumption  of  carbohydrate  and  the  produc- 
tion of  CO2,  never  absolutely  in  abeyance,  even  in  the  most  pro- 
found state  of  rest,  are  sharply  intensified  when  the  living  machine 
puts  forth  its  full  power  ;  and  there  is  then  a  sudden  burst  of 
heat,  and  an  electrical  discharge,  by  reason  of  an  electro-positive 
state  of  the  active  muscle  giving  birth  to  a  current  of  action 
which  in  effect  you  may,  without  great  stretch  of  thought,  regard 
as  of  the  family  of  blaze-currents.  So  that  in  last  resort  we  find 
that  these  striking  electrical  effects  in  living  matter  that  we  had 
hardly  considered  as  electro-motive  at  all — in  the  eyeball,  in  its 
crystalline  lens,  in  a  bean  or  pea  or  leaf  or  flower — are,  after  all, 
intense  local  changes,  significant  of  intense  local  action,  that  may 
be  imagined  and  characterised  as  a  blaze  amid  the  smouldering 
state  of  living  matter. 

There  is  a  certain  similarity  between  a  blaze-current  and 
the  discharge  of  an  electrical  organ — no  very  close  and  detailed 
resemblance  indeed,  yet  one  that  cannot  be  ignored,  and  that 
may  be  of  service  to  us  towards  a  further  comprehension  of  the 
electrical  signs  of  life.  But  it  will  not  be  an  easy  matter  to 
appreciate  the  connection,  and  in  preparation  for  the  attempt, 
I  should  advise  you  to  read  two  papers  by  du  Bois-Reymond, 
the  first  on  "  Secondary  Electromotive  Phenomena  in  Nerve, 
Muscle,  and  Electrical  Organ,"  the  second  on  "  The  Polarisation 
Phenomena  caused  by  Constant  Currents  in  the  Electrical  Organ 
of  Torpedo." 

And  let  me  say  in  conclusion  that  I  have  not  named  these 


IV.]  '  ELECTRICAL  ORGANS  75 

papers  to  you  because  either  nerve  or  muscle  or  electrical  tissue 
are  favourable  objects  upon  which  to  demonstrate  blaze-currents 
— they  are,  in  fact,  among  the  least  favourable  objects  for  this 
purpose — but  because  their  secondary  electromotive  action  or 
response,  as  described  by  du  Bois-Reymond,  presents  points  of 
similarity  with  the  currents  that  are  now  engrossing  our 
attention. 

Those  of  you  who  do  not  read  German  may  refer  to  the 
Translations  of  Foreign  Biological  Memoirs  (Oxford,  1887), 
edited  by  J.  Burdon-Sanderson.  And  any  one  who  is  specially 
interested  in  the  phenomena  of  electrical  fishes  should  also 
read  in  the  original  the  two  memoirs  by  Gotch,  published 
fifteen  years  ago  in  the  PJiilosophical  Transactions.  For  a 
student  preparing  for  examination,  the  general  summary  by 
Gotch  in  Schafer's  Text-book  of  PJiysiology  will  be  more  than 
sufficient. 


REFERENCE3 


Du   Bois-Reymond. — "  Ueber   secundarelektromotorische    Erscheinungen 

am  Muskeln,  Nerven,  und  Elektrischen  Organen,"  du  Bois-Reymond'' s 

Archiv,  p.  i,  1884. 
Du  Bois-Reymond. — "  Lebende  Zitterochen  zu  Berlin."    Ibid.,  p.  86,  1885. 
GOTCH.^ — "  The  Electromotive  Properties  of  the  Electrical  Organ  of  Torpedo 

Marmorata,"  Phil.  Trans.  Roy.  Soc,  p.  487,  1887,  and  p.  329,  1888. 
Gotch. — "The  Physiology  of  Electrical   Organs,"  Schdfe7's  Text-book  of 

Physiotogy,  vol.  ii.,  p.  561,  1900. 


LECTURE  V 

The  Discharge  of  an  Electrical  Organ  in  Response  to  Direct  Excitation — Du 
Bois-Reymond's  Summary — Similarity  between  "  Blaze-currents  "  of  the 
Skin  and  "  Discharges "  of  an  Electrical  Organ — Normal  Direction 
of  the  Organ-current — A  Speculation  and  some  Experiments — Further 
Investigation  of  these  Currents  by  the  ABC  Method — The  Positive 
Polarisation  of  du  Bois-Reymond — The  Polar  After-currents  of  Hering 
and  of  Biedermann — Ritter's  Tetanus  and  the  Post-anodic  Action 
Currents. 

§  47.  Electrical  organs. — We  shall  take  a  point  of  departure 
from  the  diagram  on  p.  121  of  the  second  paper  by  du  Bois- 
Reymond,*  where  he  gives  a  summary  of  the  effects  of  direct 
electrical  excitation  of  an  excised  portion  of  the  electrical  organ 
of  torpedo  marmorata. 

The  prefix  "  absolutely "  in  du  Bois'  terminology  is  used 
with  reference  to  the  organ  discharge,  the  response  being 
denoted  as  "  absolutely  positive "  or  "  absolutely  negative," 
according  as  it  is  in  the  same  direction  as  the  normal  discharge, 
or  of  opposite  direction. 

The  prefix  "  relatively "  refers  to  the  direction  of  response 
with  reference  to  the  exciting  current,  "  relatively  positive  "  and 
"  relatively  negative  "  signifying  that  the  response  is  in  the  same 
and  in  the  opposite  direction  to  that  of  the  exciting  current. 
If  you  are  puzzled  by  these  expressions,  or  doubt  my 
rendering  of  them,  you  should  refer  to  the  original  paper. 
Negative   polarisation   is   of  contrary  direction   to   that  of  the 

*  Archiv,  1885. 
76 


LECT. 


v.] 


ELECTRICAL  ORGANS 


77 


exciting  current ;   positive  polarisation  is  in  the  same  direction 
as  the  exciting  current. 

These   four   stages   are   reducible   to   two,   by   omission  of 
Type   IL   (variety  below   Type   I.)   and  of  Type    IIL   (variety 


The  response  is  absolutely     The  response  is  absolutely 
and  relatively  positive.  and  relatively  negative. 


fiH 


5f^ 


1[ 


PpnBmnn^ 


m 


w 


iteTITTrTT.T,^^ 


The  response  is  absolutely  positive  and  relatively 
negative. 

Fig.  34. — Du  Bois-Reymond's  diagram  (^Aix/iiv,  1885,  p.  121)  to  illustrate  the 
electrical  response  to  electrical  excitation  of  a  strip  of  the  electrical  organ  of  Torpedo. 
The  direction  of  the  normal  organ-discharge  is  supposed  to  be  upwards,  so  that  the 
first  two  responses  of  the  upper  line  are  homodrome  in  relation  to  the  exciting 
current ;  the  next  two  responses  and  all  four  responses  of  the  lower  line  are 
antidrome. 


above  Type  IV.).  We  thus  have  Type  L  as  the  characteristic 
response  of  the  living  organ,  and  Type  IV.  as  that  of  the  dead 
organ.  This— if  you  will  carefully  read  du  Bois'  description, 
and  clearly  appreciate  the  significance  of  his  terminology — 
is  the  essential  pair  of  features  that  respectively  characterise 
the  living  and  dead  states  of  an  electrical  organ — it  discharges 
in  a  direction  of  its  own  while  it  is  alive ;  after  death,  it  exhibits 
the  ordinary  polarisation  of  a  non-living  electrolyte. 


THE  SIGNS  OF  LIFE 


[lect. 


The   response  of  skin  is   on    a    precisely  similar    schema, 
thus  : — 


ELecbrLcal     oiyan 
of  Torpedo. 


Dorsum 


Venter 

Frog's  Skin 

Eoct.  surfc3.ce ' ' 

Inb.  surface 


'<it>':& 


.1.5 
II 

L:~ 

+ 

I    anUdrome 

r 

I    homodrome 

\  anbidrome 

r 

L 

" 

Response   of 
living  organ. 

PolarlsaMion 
currents  of - 
dead   organ. 

Fig.  35. — Diagram  exhibiting  the  similarity  between  an  electrical  organ  and  the 
skin  as  regards  their  normal  electrical  responses  during  life  (and  the  polarisation 
effects  after  death). 

And  as  you  see  from  the  diagram  (or  from  the  experiment  that 
is  set  up  to  reproduce  it),  we  are  justified  in  saying  of  the  skin 
that  it  discharges  in  a  direction  of  its  own  while  it  is  alive,  and 
exhibits  after  death  the  ordinary  polarisation  of  a  non-living 
electrolyte.  It  responds  better,  as  you  may  notice,  to  an  anti- 
than  to  a  homodrome  excitation,  agreeing  in  this  respect  with 
the  organ  of  Malapterurus  (Gotch),  but  disagreeing,  I  may  add, 
from  that  of  Torpedo  (du  Bois-Reymond). 

§  48.  The  organ-discharge. — The  essential  component  of  an 
electrical  organ  is  a  disc,  upon  one  surface  of  which  a  nerve 
twig  ramifies,  while  the  other  surface  is  vascular.  The  electrical 
organ  consists  of  piles  of  such  discs,  surface  to  surface,  like  the 
elements  of  an  old-fashioned  voltaic  pile ;  its  structure,  as  well 
as  the  great  electro-motive  force  of  the  discharge,  suggest  that 


v.]  THE  ORGAN-DISCHARGE  79 

it  actually  is  a  battery  of  which  the  elements  (discs)  are  dis- 
posed in  series.  Further,  the  direction  of  discharge,  excepting 
in  the  somewhat  doubtful  case  of  Malapterurus,  is  always  such 
that  current  passes  (in  the  animal)  from  the  nervous  to  the 
vascular  surfaces  of  the  discs.  Thus,  in  Torpedo,  where  the 
nervous  surface  is  ventral  and  the  vascular  surface  dorsal, 
the  discharge  is  from  venter  to  dorsum.  In  Gymnotus  the 
nervous  surface  is  posterior,  and  the  discharge  is  from  tail  to 
head.  In  Raia  (the  skate,  which  possesses  a  well-formed,  if 
attenuated,  pair  of  electrical  organs)  the  nervous  surface  is 
anterior,  and  the  discharge  is  from  head  to  tail.  This  relation 
between  position  of  nervous  plate  and  direction  of  discharge 
is  called  after  its  discoverer  "  Pacini's  law."  The  discharge  is 
attributable  to  a  sudden  action  of  the  nervous  surfaces,  which, 
while  active,  play  the  part  of  a  series  of  zinc  plates  in  a 
voltaic  pile.  The  electro-motive  force  in  the  discharge  of  a 
single  disc  has  been  estimated  to  be  0.03  to  0.05  volt,*  and 
it  is  by  reason  of  their  columnar  arrangement  and  large 
number,  that  the  high  electro-motive  values  of  the  organ- 
discharge  are  reached — 200  volts  from  a  column  of  500  plates 
is  an  E.M.F.  estimated  by  Gotch  and  Burch  in  the  case  of 
Malapterurus. 

The  discharge  can  be  brought  about  experimentally  by 
indirect  (reflex)  and  by  direct  excitation.  If,  as  was  first  done 
by  du  Bois-Reymond,  a  longitudinal  strip  of  organ  be  excised, 
placed  between  unpolarisable  electrodes,  and  directly  excited, 
it  will  respond  to  both  directions  of  excitation  by  a  discharge  in 
one  given  direction,  that  namely  of  the  normal  discharge.  This 
photographic  record  (Fig.  36)  gives  the  responses  (both  in  head 
to  tail  direction)  to  induction  shocks  in  positive  and  negative 
directions,  in  the  case  of  a  portion  of  the  rudimentary  (or 
vestigial)  organ  of  the  skate.  The  similarity  between  these 
effects  and  the  effects  above  described  in  the  case  of  the  eyeball 
and  the  skin,  are  sufficiently  obvious,  and  you  will  readily  under- 
stand how  it  has  come  about  that  I  have  compared  the  "  blaze- 
currents  "  of  the  eyeball,  and  of  the  skin,  and  of  other  organs 

*  Gotch,  Schiife7^s  Text- Book  of  Physiology,  vol  ii.,  p.  584. 


80 


THE  SIGNS  OF  LIFE 


LEcr. 


with  the  discharges  of  an  electrical  organ.  I  do  not  mean  to  say 
that  eyeball  or  skin  are  specifically  "  electrical  organs,"  for  there 
are  no  structural  features  in  common ;    but   I   think  that  the 


voLt 
■oio 


•O03 


A 


m.  h.       m.  b. 
Tetan.  1,000 


i.       1 

S'mgLe  shocks  i,opoo 


o 


10 


15 


20  mins. 


Fig.  36. — Normal  (head  to  tail)  discharges  of  a  strip  of  the  electrical  organ  of  a 
skate  (^Raia  clavatd)  in  response  to  tetanisation  and  to  strong  single  break  induction 
shocks. 

comparison  goes  some  way  towards  generalising  our  notion 
of  the  electrical  signs  of  life.  It  is  at  least  remarkable  that  the 
electro-motive  values  of  the  discharge  in  the  cases  of  the  eye- 
ball and  of  the  skin  are  of  the  same  order  of  magnitude  as  that 
calculated  for  a  single  plate  of  the  electrical  organ  (0.03  to  0.05). 
According  to  a  recent  estimate  by  Gotch,*  the  E.M.F.  of  nerve 
in  response  to  a  single  induction  shock  reaches  a  value  not  far 
short  of  this — viz.,  0.03  volt.  And  the  very  points  where 
the  comparison  is  defective  should  serve  to  instigate  further 
study.     Thus  the  organs  of  Torpedo,  Gymnotus  and  Raia  are 


*  Gotch  and  Burcli,  Proc.  Roy.  Soc.^  vol.  63,  p.  300,  il 


v.]  ,  DIRECT  RESPONSE  81 

modifications  of  muscle.*  The  organ  of  Malapterurus  (which 
does  not  follow  Pacini's  law)  is  a  modification  of  cutaneous 
gland  ;  we  therefore  want  to  examine  that  organ  by  the  light  of 
what  we  have  learned  of  skin.  Does  the  electrical  case  of 
Malapterurus  give  an  outgoing  current  ?  Perhaps  one  of  these 
days  we  shall  have  an  opportunity  of  finding  out. 

Meanwhile  let  me  warn  you  that  our  knowledge  of  even 
the  most  carefully  studied  of  electrical  organs — that  of  Torpedo, 
namely — is  by  no  means  exhaustive.  Its  discharge  is  of  very 
short  duration  ;  one  may  feel  an  intense  thrill  from  a  discharge 
giving  by  no  means  an  excessive  effect  upon  a  galvanometer ; 
the  organ  itself  while  reacting  perfectly  well  to  indirect  excita- 
tion, is  peculiarly  refractory  to  direct  electrical  excitation.  This 
same  peculiarity  is  exhibited  by  the  excised  organ  or  by  strips 
of  organ  from  even  the  most  lively  fish,  and  I  have  failed  to 
obtain  from  such  strips  any  well-marked  response  to  single 
induction  shocks  ;  I  had  to  use  tetanising  currents  to  bring  out 
any  regular  venter-to-dorsum  response  ;  the  organ  was  easily 
exhausted,  and  easily  injured,  by  e.g.^  removal  of  the  skin, 
which  is  closely  attached  to  it  ;  obviously  an  effect  obtained 
only  in  the  presence  of  skin,  and  not  obtained  after  its  removal, 
might  not  straightway  be  set  down  as  "  organ-response " ;  I 
have  indeed  seen  similar  responses,  of  a  value  of  H- 0.005  volt, 
with  strips  of  fish  that  contained  no  electrical  organ  at  all,  but 
only  muscle  between  two  layers  of  skin. 

So  that  on  the  whole  the  case  of  the  electrical  organ  is  a 
good  deal  less  satisfactory  than  that  of  the  skin,  and  in  com- 
paring the  skin  and  the  eyeball  with  an  "  electrical  organ,"  we 
use  the  expression  in  a  general  rather  than  in  a  special  sense.  As 
regards  blaze-currents,  the  skin  of  a  frog  is  a  far  more  efficient 
electrical  organ  than  is  the  electrical  organ  of  a  Torpedo.  And 
perhaps  this  is  not  so  very  unfortunate  ;  you  may  easily  control 
statements  concerning  the  frog's  skin,  you  would  have  to  take 

*  Developmentally,  inasmuch  as  muscle  and  electrical  organ  come  from 
the  same  muscle  plates  ;  and,  in  the  skate,  muscle  shades  into  organ  by 
gradual  transition.  Gotch  considers  the  electrical  organ  to  be  a  nerve- 
ending.     But,  in  a  sense,  muscle  itself  is  a  nerve-ending. 

F 


82  THE  SIGNS  OF  LIFE  [lect. 

a  good  deal  of  trouble  if  you  wanted    to   control   statements 
concerning  the  Torpedo. 

§  49.  Its  direction. — The  direction  of  response  to  stimuli  of 
both  directions  is  an  indication  of  the  natural  direction  of 
organ  response.  The  strip  of  organ  discharges  in  the  way 
determined  by  its  structural  and  functional  disposition.  Can  we 
trace  any  analogous  disposition  in  the  case  of  the  analagous 
response  of  eye  or  skin  ?  May  we  consider  that  the  direction  of 
a  blaze-current  is  in  any  measure  determined  by  structural  and 
functional  disposition  of  organ  ;  or,  otherwise  expressed,  have  we 
any  right  to  attribute  an  organ-current  to  such  structures  ?  I 
think  there  are  reasons  for  and  reasons  against  an  affirmative 
answer.  As  regards  the  eye,  we  have  positive  response  to  light 
and  positive  response  to  both  directions  of  electrical  excitation. 
We  also  have  negative  response  to  light  and  negative  response 
to  both  directions  of  electrical  excitation.  But  here  is  no 
definite  and  fixed  direction  of  organ-discharge,  only  a  pre- 
dominance, fluctuating  with  state  of  organ  and  kind  of  animal. 

§  50.  TJie  skin-discharge.  —  As  regards  the  skin,  we  have 
positive  response  and  negative  response  to  indirect  excitation, 
and  almost  exclusively  positive  (outgoing)  response  to  direct 
electrical  excitation  of  whatever  direction.  Here,  again,  is  no 
definite  and  fixed  direction  of  organ-discharge  by  the  natural 
mode  of  action  through  nervous  channels,  but  a  marked  pre- 
dominance in  one  (the  outgoing)  direction  in  response  to  both 
directions  of  electrical  excitation. 

With  direct  excitation  of  the  skin,  we  must  suppose  that  all 
its  living  parts  are  aroused  to  action,  gland  cells  and  general 
epithelium  alike,  and  we  may  not  attribute  the  effect  to  any  one 
kind  of  tissue  element  to  the  exclusion  of  others.  We  know  by 
experiment,  however,  that  the  action  proceeds  from  elements 
at  or  near  the  external  surface  ;  and  we  find  further  that  with 
shavings  of  skin,  including  Malphigian  layer  and  excluding  the 
deeper  situated  glands,  the  direct  response  is  obtained  as  before, 
while  with  shavings  of  cuticle  only,  no  response  whatever  is 
obtained.     Mercuric  chloride,  which,  as  you  saw,  abolished  the 


v.] 


THE  SKIN  DISCHARGE 


83 


direct  response,  is  said  by  Bach  and  Oehler  not  to  abolish  the 
indirect  excitabihty,  which  presumably  depends  on  deeper  parts. 
We  therefore  conclude  that  the  main  factor  of  the  response  is 
the  general  epithelial  investment  —  its  Malpighian  layer  in 
particular.  Indirect  excitation  of  the  skin  through  nervous 
channels  presumably  arouses  the  cutaneous  glands  alone ;  the 
general  epithelium  is,  as  far  as  we  know,  as  much  outside  the 
control  of  nerve  fibres  as  are  blood-corpuscles. 

We  cannot,  therefore,  in  comparing  the  effects  of  direct  and 
of  indirect  excitation,  regard  the  comparison  as  a  simple  one, 
like  that  of  direct  and  indirect  excitation  of  muscle. 

Thus,  in  frog's  skin,  the  effect  of  indirect  excitation  is  often 
negative  (ingoing)  when  that  of  direct  excitation  is  positive 
(outgoing).  In  cat's  skin  the  effect  of  indirect  excitation  is 
always  ingoing,  that  of  direct  excitation  is  at  first  ingoing,  at 
last  outgoing. 

It  would  be  interesting  to  see  what  effect,  if  any,  the  two 
forms  of  excitation  exercise  upon  each  other.  I  have  not  found 
time  to  do  this,  although  obviously  it  would  be  an  easy  matter 
to  take  a  regular  series  of  indirect  effects,  interpolating  in  the 
series  one  or  more  direct  excitations  of  some  convenient  duration 
and  strength ;  or  a  regular  series  of  direct  effects,  interpolating 
in  the  series  one  or  more  indirect  excitations.  Of  course,  it 
would  be  necessary  to  photograph  the  effects ;  I  wonder  what 
they  would  be  ?  * 

*  I  have  since  tested  this  point,  as  regards  the  effect  of  direct  upon 
indirect  excitation,  in  the  case  of  frog's  skin,  also  in  the  case  of  the  cat 
{vide  infra,  Lecture  VI.),  with  the  following  results  : — 

VoU 

•005-1 

•004-- 

•003 

■OOZ 

■OOI 

■000 

Before 

Fig.  37. — Indirect  responses  of  frog's  skin  to  tetanisation  of  the  sciatic  nerve 
before  and  after  direct  excitation  of  the  skin  itself  by  a  single  strong  induction 
shock  D. 

[For  conthmation  of  Note  ^  see  next  page. 


84 


THE  SIGNS  OF  LIFE 


[lect. 


So  that,  in  sum,  while  pointing  to  the  conclusion  that 
there  is,  as  regards  the  external  cover  of  an  animal  body, 
an  outgoing  organ-current  of  action,  the  facts  forbid  us  to 
rest  content  in  an  exclusive  conclusion  of  such  simplicity,  and 
we  are  obliged  to  admit  that  a  cutaneous  organ-current,  even  if 
it  really  exists  by  reason  of  a  general  functional  and  structural 
organisation  of  the  integument,  is  twisted  and  obscured  by  other 
accessory  and  complicating  conditions. 

Let  us,  however,  imagine  how  things  might  have  been.  The 
fancy  will,  if  nothing  else,  remind  us  of  facts,  and  make  us 
curious  for  further  facts.  The  facts — let  me  reiterate  them  once 
more — are  that  the  skin,  when  first  placed  on  the  electrodes, 
gives  an  ingoing  current  which  increases,  and  that  excitation  of 
either  direction  gives  an  outgoing  response  which  diminishes. 
The  former  is  "current  of  rest,"  the  latter  "current  of  action." 

§  51.  ^  speculation. — A  lump  of  protoplasm,  at  rest  and 
homogeneous  throughout,  is  iso-electric  throughout  ;    let  it  be 


VoLb 

■  0000- 

■  0025- 
■ OOSO- 
'007S- 
•OJOO- 
'0/25-^ 


D., 


jVfilY'^ffT''^^^^^ 


4 


A, 


Fig.  38. — Indirect  responses  of  a  pad  of  a  cat's  paw  to  single  induction  shocks 
exciting  the  sciatic  nerve,  before  and  after  : — 

D,   —  direct  excitation  of  the  pad  by  one  strong  break  shock. 
D„  =  „  ,,  by  two  strong  break  shocks. 

Dg   =  ,,  ,,  by  tetanisation  for  5  seconds. 

D4  =  ,,  ,,  by  tetanisation  for  15  seconds. 

It  is  somewhat  surprising  that  direct  excitation  should  have  produced  a 
greater  diminution  of  the  indirect  response  in  the  frog  than  in  the  cat.  But 
in  the  former  case  the  indirect  response  was  elicited  by  tetanisation  of  the 
nerve,  while  in  the  case  of  the  cat,  the  nerve  was  excited  by  single  strong 
shocks.  The  regular  effects  (on  the  skin  glands)  of  such  stimulation  are  in 
themselves  sufficiently  remarkable  ;  their  true  physiological  character  was 
proved  by  the  long  interval  between  each  excitation  and  response — about 
3  seconds. 


v.] 


EXTERNAL  AND  INTERNAL 


85 


"  Current  of  rest  "  from  E  to  I. 
"  Current  of  action  "  from  I  to  E. 


acted  upon  by  its  environment,  any  point  of  its  surface  E  is 
chemically  more  active  than  any  point  of  its  mass  I ;  E  becomes 
electro-positive  to  I ;  there  is  therefore  current  from  E  to  I,  an 
ingoing  current,  the  so-called  "  current  of  rest."      Let  the  lump 

become  active,  any  point  I  is 
chemically  more  active  than  any 
point  E  ;  there  is  current  from 
I  to  E,  outgoing  current,  the 
"  normal  organ-current  of  action." 
Now,  the  currents  that  we  call 
"  electrical "  and  actual  currents  of 
matter,  streaming  through  a  porous 
substance,  generally  occur  in  the 
same  direction,  so  that  there  is  an  association  of  phenomena 
— (i)  in  the  case  of  ingoing  electrical  current  and  centripetal 
current  of  matter  (and  of  energy)  from  environment  to  living 
substance,  and  (2)  in  the  case  of  outgoing  electrical  current 
and  centrifugal  current  of  matter  (and  of  energy)  from  living 
substance  to  environment.  A  priori,  therefore,  we  should 
expect  the  "  skin "  of  living  substance  to  be  the  channel  of  a 
double  current,  material  and  electrical — (i)  of  a  current  of  rest 
or  reception,  ingoing  and  centripetal,  subserving  the  synthetic 
accumulation  of  energy  ;  (2)  of  a  current  of  action  or  emission, 
outgoing  and  centrifugal,  subserving  the  analytic  expenditure 
of  energy.  If  you  are  accustomed  to  think  in  terms  of  charged 
ions,  you  will  imagine  the  kation  as  travelling  from  without 
inwards  with  a  receipt  of  energy,  from  within  outwards  with  a 
discharge  of  energy. 

And  now  consider  further  what  kind  of  modifications  we  may 
expect  and  look  for  with  the  differentiations  of  function  and 
of  structure  that  have  occurred  in  the  external  surface  of  plants 
and  animals. 

Consider,  in  first  place,  the  principal  difference  of  chemical 
direction  in  the  main  drift  of  vegetable  and  of  animal  metabolism. 
Vegetable  protoplasm"  is  in  major  degree  an  instrument  of  syn- 
thesis and  accumulation,  in  minor  degree  the  seat  of  analysis 
and  emission.  Animal  protoplasm  is  in  major  degree  an  instru- 
ment of  analysis  and  emission,  in   minor  degree  the  seat   of 


86  THE  SIGNS  OF  LIFE  [lect. 

synthesis  and  accumulation.  The  vegetable,  in  most  immediate 
contact  with  inert  things,  combines,  organises,  and  accumulates. 
The  animal,  in  less  immediate  contact  with  inert  matter,  disrupts, 
utilises,  and  dissipates  in  their  fragments  organic  compounds 
that  it  has  received  ready-made  from  other  animals  and  from 
plants.  And  quite  early  in  its  development  the  external  surface 
of  the  animal  is  distinguishable  into  two  parts:  (i)  a  surface 
principally  receptive  of  incoming  matter,  the  digestive  and 
absorbent  surface ;  (2)  a  principally  emissive  surface,  the  ex- 
ternal skin,  through  which  the  greater  moiety  of  animal  energy 
is  dissipated.  An  "  organ-current  of  action,"  if  aroused  in  these 
surfaces,  should,  according  to  their  several  physiological  habits 
and  dispositions,  be  : — 

Principally  ingoing  for  the  vegetable  "  skin." 
Principally  outgoing  for  the  animal  skin. 
Principally  ingoing  for  the  animal  mucosa. 

§  52.  Some  experiments. — And  whatever  the  fate  of  our 
theoretical  motive,  it  will  have  served  to  instigate  a  search  for 
facts ;  but  we  must  take  due  care  to  emancipate  observation 
from  expectation,  and  not  merely  see  that  which  we  expect 
or  hope  to  see.  Here  is  a  piece  of  orange  peel,  chosen  for  our 
purpose  not  merely  because  it  is  a  handy  object,  but  because  the 
"  skin,"  presumably  living,  is  easily  separated  from  the  "  body " 
of  the  fruit  by  breaking  through  "  subcutaneous  tissue,"  pre- 
sumably not-living.  And  in  point  of  fact,  you  notice  that  the 
bit  of  orange  peel,  placed  between  unpolarisable  electrodes, 
exhibits  little  or  no  current,  unlike  a  paring  of  an  apple  or  a 
potato  that  necessarily  has  an  injured  inner  surface,  and  ex- 
hibits, therefore,  a  strong  outgoing  current  of  injury.  I  com- 
pensate precisely  and  then  test  in  the  way  now  familiar  to  you 
(plug  the  galvanometer,  send  an  induction  shock  through  skin, 
unplug  the  galvanometer),  and  you  see  that  to  both  -f  and  — 
directions  of  excitation  the  orange  peel  responds  by  a  deflection 
to  your  left,  signifying  current  of  negative  or  ingoing  direction. 

§  53.  Human  skin.  —  I  next  take  a  piece  of  human  skin, 
twenty-four  hours  after  excision,  and  test  it  in  the  same  way 


v.]  ,  MUCOUS  MEMBRANES  87 

by  +  and  —  break  induction  shocks.  You  see  that  to  both 
directions  of  excitation  the  response  has  been  a  deflection 
to  your  right,  signifying  current  of  positive  or  outgoing  direc- 
tion. 

§  54.  Mucous  vievibranes. — These  two  experiments  are  in 
accord  with  our  theoretical  forecast,  but  that  they  prove  that 
forecast  to  be  a  true  guess,  or  even  bear  it  out  to  any  serious 
extent,  I  shall  be  the  last  to  urge.  The  two  facts  (both  of 
which  are  representative  results  based  upon  a  sufficient  number 
of  trials)  are,  however,  interesting  in  themselves,  whether  this 
or  any  other  explanation  be  the  true  one.  With  regard  to  the 
digestive  mucosa,  I  prefer,  for  lack  of  sufficient  experience,  not 
to  show  you  any  experiment  at  all,  for  I  am  at  present  by  no 
means  sure  what  is  to  be  considered  as  a  typical  and  what  as 
an  exceptional  result.  I  have  seen  ingoing  response  more 
frequently  than  outgoing  response,  but  I  desire  to  study  the 
conditions  and  magnitude  of  the  response  before  coming  to 
any  conclusion  as  to  which  is  the  typical  one.* 

I  would  rather  show  you  another  pair  of  experiments, 
illustrating  in  a  different  way  the  apparent  opposition  of 
direction  in  the  blaze-currents  of  vegetable  and  of  animal 
"  skins." 

I  55.  Intact  surfaces.  —  We  want  to  test,  e.g.,  the  skin  of 
an  animal,  or  of  a  vegetable,  without  previous  injury  of  the 
surface.  A  very  little  reflection  will  convince  us  that  this  can 
only  be  done  by  applying  what  has  already  been  alluded  to 
above  as  the  ABC  method,  viz.,  stimulating  through  A  B,  and 
leading  off"  through  either  A  or  B  and  a  third  indifferent 
point  C  (p.  69). 

The  three  electrodes,  ABC,  are  applied  to  three  separate 
external  spots  of  a  piece  of  frog's  skin.     I  intend  to  test  the 

*  From  further  observations  made  subsequently  to  the  dehvery  of  these 
lectures,  I  think  the  above  statements  may  be  considerably  hardened. 
In  the  great  majority  of  cases — so  great  that  we  may  reckon  an  opposite 
result  as  exceptional — the  mucosas  manifest  ingoing  response  to  both 
directions  of  excitation. 


88  THE  SIGNS  OF  LIFE  [lect. 

point  B,  so  I  compensate  B  C,  then  excite  through  A  B,  and  then 
lead  off  B  C  to  the  galvanometer,  as  shown  in  Fig.  33.  You 
note  the  deflection.  I  repeat  the  experiment  with  excitation 
in  the  reverse  direction ;  again  you  note  the  deflection.  I 
repeat  a  similar  pair  of  trials  upon  another  point  A,  merely 
to  get  a  further  pair  of  observations- — compensating  A  C,  ex- 
citing through  A  B,  and  leading  off  through 
A  C.  You  have  noted  the  deflections,  f-^^-  ^  ^  ^ 
both  the  B  C  deflections  to  your  left,  and   Resp:   < 

the  A  C  deflections  to  your  right,  thus  : —  \  

signifying — as   you   will   easily  verify — in  ^ 

all  four  instances  that   the  after-effect  at  '*' 

A  or  at  B,  whether  anode  or  kathode  of  "*  ~-— ^ 

the  exciting  current,  has  been  outgoing. 

Repeating  a  similar  series  of  four  trials  with  an  apple — a 
living  apple  of  course — and  noting  the  deflections  as    before, 
you    find    that    they    are    in    every    case 
the  other  way  round,  viz.,  both  B  C  deflec-    Eccc-.  -^         ^         ^ 
tions  to  your  right,  both  A  C  deflections    ^^^P-  — *■ 

to  your  left,  like  this  : —  ■<  

signifying  in  all  four  instances  that  the  after- 
effect at  A  or  at  B,  whether  anode  or  kathode  < 

of  the  exciting  current,  has  been  ingoing.  -< ^ 

Now,  is  not  this  an  interesting  result, 
and  does  it  not  come  out  very  clearly  on  this  system  of 
notation?  In  my  first  attempts  to  examine  one  of  two  stimu- 
lated points  by  conjoining  it  through  the  galvanometer  with  a 
third  indifferent  point,  I  found  it  very  troublesome  to  take 
notes  correctly,  very  difficult  to  read  notes  when  taken,  and 
quite  impossible  to  realise  during  an  observation,  what  was 
the  meaning  of  each  individual  deflection.  But  since  I  have 
followed  and  become  familiar  with  this  system  of  notation,  all 
these  drawbacks  have  disappeared,  and  we  may  read  and 
compare  at  a  glance  "  formulse  of  response  "  of  a  great  variety 
of  living  things. 

I  shall  not  enter  into  further  explanations  now ;  the  method 
will  be  used  again,  and  more  fully  explained  in  a  future  lecture, 
and  then  appreciated  by  you  as  a  simplification,  if  meanwhile 


y.J  ,     "  POSITIVE  POLARISATION "  89 

you  will  puzzle  the  thing  out  for  yourselves.  To  save  space,  the 
formulae,  which  to  show  order  of  individual  trials  have  been  set 
out  as  above,  will  sometimes  be  given  thus  : — 

Frog's  skin.  Fruib  shin. 


§  56.  Positive  polarisation. — Let  us  now  turn  our  attention 
to  another  related  subject,  that  of  positive  polarisation,  and  of 
post-anodic  (and  post-kathodic)  action-currents. 

Du  Bois-Reymond  obtained  his  first  inkling  of  "  positive 
polarisation"  in  1843,  but  it  was  not  till  1883  that  he  published 
a  full  account  of  the  subject.  He  introduces  that  account  in 
the  following  terms,  which  clearly  indicate  the  place  held  by  the 
matter  in  his  thoughts : — 

"  I  consider  that  the  time  has  come  to  break  the  silence  which  I  have 
preserved  till  now  concerning  certain  electi'o-physiological  experiments  that 
have  engaged  my  attention  for  nearly  forty  years,  and  to  which  I  attribute 
very  great  importance." 

Taking  the  case  of  muscle,  he  studies  the  secondary  polari- 
sation effects  produced  by  strong  constant  currents,  tabulating 
his  results  in  relation  to  current-strength  and  time  of  closure ; 
and  how  laborious  a  task  this  was  du  Bois'  own  words  will  most 
vividly  bring  before  you. 

"The  preparation  of  such  a  table  of  data  is  a  very  wearisome  under- 
taking. The  secondary  effects  of  currents  that  are  at  all  strong  or  long,  are 
for  the  most  part  so  enduring  that  a  fresh  preparation  is  required  for  nearly 
each  single  experiment  .  .  .  each  fresh  preparation  requires  a  fresh  frog  ■ 
.  .  .  to  permit  of  comparison,  the  frogs  must  be  as  uniform  as  possible  in 
size  and  health.  ...  So  that  the  completion  of  a  table  of  data  is  the 
work  of  many  weeks,  and  it  will  therefore  hardly  be  matter  for  surprise  that 
I  have  only  twice  accomplished  the  task,  once  in  the  autumn  of  1855,  once 
in  the  summer  of  1882." 

Each  such  table  comprised  200  successful  observations, 
with  currents  of  i  Daniel  to  40  Groves,  and  closure  times  of 
0.006  sec.  to  25  minutes.  The  polarisation  currents  were  of  two 
kinds  : — negative,  first  visible  after  a  current  of  i  Daniel  passed 
for  a   period   of   i    sec. ;   positive,  requiring  at  least  2  Groves 


90 


THE  SIGNS  OF  LIFE 


[lect. 


with  a  closure  time  of  0.3  sec.  The  strongest  negative 
polarisation  occurred  after  a  current  of  i  Daniel  passed  for  10 
minutes ;  the  strongest  positive  polarisation  after  a  current  of 
20  Groves  passed  for  0.075  sec. ;  in  the  latter  case  the  E.M.F. 
appeared  to  be  rather  less  than  that  of  a  muscle-current. 


Fig.  39. — T  is  the  time  of  closure,  A  the  density  of  the  polarising  current, 
+  S  the  strength  of  the  secondary  electromotive  effect,  so  that  the  plane  viewed  in 
perspective  is  the  T  A  Plane.  The  individual  ordinates  S  are  not  represented, 
but  only  the  curves  joining  the  ordinates  belonging  to  given  current  density  and  given 
time  (from  du  Bois-Reymond,  Archiv,  1884,  p.  15). 


§  57.  Two  criticisms. — Hermann — du  Bois'  former  pupil  and 
untiring  critic — pounced  at  once — -showing  and  saying  in  a 
paper  of  upwards  of  sixty  closely  printed  pages  of  Pfliige7''s 
Archiv  (vol.  xxxiii.),  that  du  Bois'  positive  polarisation  current 
was  in  reality  a  post-anodic  action-current.  Hering  also  inter- 
vened, and  said  the  same  thing  in  two  successive  papers  of  the 
Wiener  Sitzungsberichte  (12th  and  13th  communications,  1883). 

Both  du  Bois'  critics  confined  themselves  to  a  discussion  of 
the  interpretation  to  be  placed  upon  du  Bois'  phenomenon,  and 
proved  that  it  was  of  post-anodic  nature,  and  that  the  designa- 
tion of  positive  polarisation  was  a  very  unhappy  one.  But  the 
critics  did  not  demur  to  or  subtract  from  the  fact  itself,  nor 


v.]  ,  THE  FOUR  AFTER-CURRENTS  91 

indeed  did  they  add  to  or  extend  it.  Indirectly,  however,  by 
the  effect  produced  in  the  mind  of  his  pupil  Biedermann, 
Hering  has  "  authorised "  a  very  considerable  extension  of 
fact  and  still  more  of  doctrine.  Biedermann  finds  evidence 
of  the  existence  not  only  of  a  positive  anodic,  but  also  of  a 
negative  kathodic  after-current,  and  further  of  the  counterpart 
of  this  first  pair,  viz.,  a  negative  anodic  and  a  positive  kathodic. 
The  last  pair  of  currents  are,  however,  asked  for  by  theory 
rather  than  offered  by  simple  observation ;  Biedermann  him- 
self admits  that  of  his  four  currents  the  positive  kathodic  is 
very  doubtful,  and  it  is  clear  that  the  negative  anodic,  being 
in  the  direction  of  ordinary  polarisation,  is  also  on  a  doubtful 
footing  of  fact.  Nevertheless  he  considers  theoretically  the  first 
pair  as  being  of  irritative  origin,  and  the  second  pair  as  being 
of  inhibitory  origin.  His  quadrille  of  after-currents  may  be 
put  together  in  the  following  schema  : — 

Excising  or  primary 

Anode    H- g^^^e^^-    ,  _  Ka.Chode 

Irritative  or      iposiCive  anodic  >  "Che  most,  cerCdin" 

dissimilatory.     {negaC/ve  kaChodic  '»"™™™       [P poLcLriscLCion] 

Inhibitory  or     \neg<^l:ive  anodic  .<-.»».  [PpoLarisaCionJ 

assimilatory.      \oosiCive  kaCfiodic  »        Che  most:  uncertain 

§  58.  ^  demonstration. — I  should  be  sorry  to  attempt  to 
demonstrate  to  you  the  existence  of  these  four  currents  upon 
muscle  or  upon  nerve,  which  are  the  tissues  upon  which  Bieder- 
mann claims  to  have  observed  them  ;  you  must  refer  to  Bieder- 
mann's  own  account  for  what  in  his  opinion  constitutes  the 
evidence  of  their  existence. 

At  most,  I  shall  be  able  to  show  you  the  first  and  "most 
certain  "  of  them,  viz.,  the  positive  anodic  or  post-anodic  action- 
current,  "and  that  only  in  a  form  that  does  not  exclude  a  partici- 
pation in  the  total  effect  of  a  positive  kathodic  factor.  And  I 
will  show  the  experiment  in  a  form  intended  to  associate  in 
your  mind  this  post-anodic  action-current  with  an  irritative 
phenomenon  long  known  to  physiologists  under  the  name  of 
Ritter's  tetanus. 


92 


THE  SIGNS  OF  LIFE 


[lect. 


Here  is  a  nerve-muscle  preparation,  the  nerve  of  which  is 
laid  across  electrodes  that  are  connected  with  the  keyboard 
and  galvanometer.      There  can  also  be  led  into  the  keyboard, 


Anode  Kd.thode 


Fig.  40. — Nerve-muscle  preparation  ;  to  demonstrate  the  muscular  contractions 
associated  with  the  positive  anodic  after-current  in  nerve. 

by  means  of  a  double  key,  a  strong  battery-current  which  is  to 
traverse  the  nerve  in  an  ascending  direction  as  figured  (the 
galvanometer  meanwhile  being  plugged).  During  the  passage 
of  the  constant  current,  the  muscle  remains  quiescent,  but  when 
I  break  the  current,  the  muscle,  as  you  see,  contracts,  and  will 
contract  for  a  longer  or  shorter  period.  Immediately  after 
breaking  the  battery  current,  I  unplug  the  galvanometer,  when 
you  witness  a  strong  and  permanent  positive  deflection,  signifi- 
cant of  an  action-current  in  the  nerve  of  the  same  direction 
as  that  of  the  previous  battery-current.  The  deflection  is  not 
absolutely  permanent,  it  is  gradually  falling,  the  muscle  will  not 
remain  indefinitely  contracted,  it  will  relax  sooner  or  later ;  the 
positive  current  in  the  nerve,  and  the  contraction  of  the  muscle, 
are  associated  effects  of  a  state  of  local  irritation  or  action  in  the 
previously  anodic  region  of  the  nerve.  You  know  that  the 
current  from  an  active  to  an  inactive  spot  of  nerve  runs  in  the 
nerve  from  active  to  inactive  (in  the  galvanometer  from 
inactive  to  active,  the  latter  pole  being  therefore  called  nega- 
tive), and  that  the  active  spot  acts  like  the  zinc  of  a  voltaic 
couple — is  in  brief  a  zincative  spot.  Therefore  you  know  from 
the  direction  of  this  after-current  that  the  active  spot  from 
which  the  irritation  to  the  muscle  proceeds  is  post-anodic  as 
to  its  source  in  the  nerve  itself 


59.  Locality  of  reactioji. — Polar  inequalities  of  effect  have 


v.]  BOTH  POLES  ARE  EFFECTIVE  93 

been  alluded  to  above,  and  now  demand  our  somewhat  closer 
scrutiny.  Is  a  blaze-current  exclusively  post-anodic  or  post- 
kathodic,  or  both,  and  if  both,  which  is  the  more  effective  pole  ? 

The  question  can  be  experimentally  tested  in  three  ways — 
the  exciting  current  can  be  sent  through  the  skin  by  two 
electrodes  in  contact  with  its  two  surfaces  (Fig.  26),  or  through 
electrodes  both  of  which  are  applied  to  the  external  surface,  or 
with  three  electrodes  A  B  C  on  the  external  surface  (Fig.  33). 

By  the  first  of  these  three  plans  we  have  already  seen  that 
with  both  directions  of  excitation  an  outgoing  response  is  pro- 
voked ;  we  have  seen  farther  (§  43)  that  both  these  responses 
depend  on  an  electro-negative  state  at  or  close  to  the  external 
surface.  Both  poles  produce  this  change,  and  the  fact  (illustrated 
by  Fig.  30)  that  the  antidrome  is  sometimes  greater  than  the 
homodrome  response,  signifies  at  first  sight  that  the  anode  is 
more  efficacious  than  the  kathode.  But  this  conclusion  is  not 
confirmed  by  our  next  two  experiments,  and  the  inequality  of 
response,  which,  indeed,  I  find  on  reference  to  my  notes,  is  by 
no  means  invariable,  may  have  been  due  to  other  causes,  e.g., 
to  ordinary  polarisation  currents  against  homodrome  and  with 
the  antidrome  response,  the  true  physiological  response  being 
greater  in  the  homodrome  sense. 

The  second  plan  of  experiment,  by  two  external  electrodes, 
gives  a  result  that  can  hardly  consist  with  superiority  of  a  post- 
anodic  effect.  The  response  in  this  case  is  always  homodrome, 
and  since  it  is  the  algebraic  sum  of  two  opposed  outgoing  currents 
at  the  two  poles,  this  signifies  that  the  kathode  has  been  more 
efficacious  than  the  anode.  A  homodrome  post-anodic  response 
would  have  been  ingoing,  but  as  we  have  seen,  and  shall  see 
again,  it  is  the  post-anodic  response  which  is  antidrome  and 
outgoing.  This  experiment  exhibiting  homodrome  response 
with  two  external  electrodes  is  easily  repeated  ;  the  result  is 
very  constant  and  contrasts  sharply  with  that  obtained  when 
the  two  electrodes  are  applied  to  the  internal  surface;  this 
surface  is  ineffective,  and  gives  only  small  antidrome  deflections 
attributable  to  ordinary  polarisation,  whereas  the  external  sur- 
face gave  large  homodrome  deflections  of  which  the  physiological 


94 


THE  SIGNS  OF  LIFE 


[^ 


integrity  of  the  skin  is  a  necessary  condition.     With  killed  skin, 
both  surfaces  give  only  the  small  counter  currents  of  ordinary 


Skin  of  Frog. 


Excited  and  led  off  by  its 
external  surface. 


Excited  and  led  off  by  its 
internal  surface. 


polarisation.  With  three  external  electrodes,  and  proceeding 
on  the  ABC  plan,  to  test  the  separate  unipolar  effects  at  A 
and  at  B  (p.  69),  the  antidrome-anodic  effect  has  sometimes 
exceeded  and  sometimes  fallen  short  of  the  homodrome- 
kathodic  effect.  The  first  inequality  proves  nothing,  as  it 
might  be  an  effect  of  ordinary  polarisation  ;  the  second 
inequality  proves,  that  under  certain  conditions,  and  in  spite 
of  ordinary  polarisation,  the  kathode  is  the  more  effective  pole. 

So  that,  in  sum,  we  may  conclude  with  certainty  that  both 
poles  are  effective,  and  with  less    certainty  that    the    kathode 

B  C         A 


i         i I 


4-^ 

Frog's  Skin. 

All  responses  are  outgoing. 
The  homodrome  kathodic  cur- 
rents I  and  4  exceed  the  anti- 
drome  anodic  currents  2  and  3. 


Vegetable  Skin. 
All    responses    are    ingoing. 
The  homodrome  anodic  currents 
2    and    3    exceed   the   antidrome 
kathodic  currents  I   and  4. 


is  more  effective  than  the  anode.     It  is  somewhat  surprising 


v.]  UNFINISHED  WORK  95 

to  have  to  admit  that  we  have  to  do  with  a  homodrome  post- 
kathodic  current.  A  homodrome  post-anodic  current  would 
have  seemed  more  famiHar  to  us. 

In  all  these  experiments,  it  is  remarkable  how  strictly  the 
effects  of  excitation  are  limited  to  the  directly  excited  spot. 
Outside  the  area  of  direct  excitation,  the  excitability  of  the 
skin  remains  unaffected ;  we  can  locally  exhaust  the  skin  by 
strong  excitation,  and  obtain  good  response  from  other  spots 
of  the  same  piece  of  skin. 

This  local  independence  of  parts,  characteristic  of  vegetable 
tissues  as  well  as  of  the  skin,  is  in  marked  contrast  with  the 
spread  of  disturbance  that  is  peculiar  to  muscle  and  nerve 
where  propagated  effects  are  the  salient  feature.  It  is  one 
of  the  reasons  why  a  piece  of  skin  or  of  a  plant  is  a  more 
favourable  object  than  a  muscle  or  a  nerve  for  the  demonstra- 
tion of  blaze-currents. 

Plants,  excited  and  led  off  by  two  points  of  their  external 
surface,  give,  like  the  frog's  skin,  homodrome  responses  to  both 
directions  of  excitation.  But  whereas  in  the  case  of  frog's 
skin,  the  total  homodrome  effect  between  A  B  is  the  alge- 
braic sum  of  the  partial  outgoing  effects  at  A  and  B,  in  that  of 
a  vegetable  skin  it  is  the  sum  of  two  ingoing  effects.  The  pre- 
potent pole,  in  the  case  of  the  frog's  skin,  was  the  kathode,  in 
that  of  the  vegetable  skin,  it  is  the  anode,  as  will  be  evident  to 
you  on  careful  consideration  of  the  figure.  It  is  not  difficult  in 
the  case  of  vegetables  to  obtain  measurements  of  the  total  and 
partial  blaze-currents,  showing  quite  clearly  that  the  anode  has 
been  the  prepotent  pole,  thus  : — 

Excitation  from  B to A 

Total  response  from       B to A  +  0.012  volt. 

Partial  response  from  B...to...C  +  0.035  »> 

Partial  response  to     C   from  A  -  0.021  „ 

Cut  surfaces  of  fruits — e.g.,  of  apples  and  pears — have  given 
ingoing  currents  at  both  poles  after  excitation,  but  smaller  than 
the  currents  aroused  at  intact  surfaces.  Ripe  orange  peel  has 
given  ingoing  effects  at  its  external  surface,  and  only  small 
polarisation  counter-currents  at  its  internal  surface,  the  former 
is  "  alive,"  the  latter  is  "  dead." 


96  THE  SIGNS  OF  LIFE  [lect.  v. 

§  60.  Exposed  muscle  has  given  precisely  the  same  formula 
as  that  of  vegetables,  i.e.,  ingoing  effects  at  both  poles ;  while 
dead  muscle  gave  only  the  small  antidrome  deflections  due  to 
ordinary  polarisation, 

A  frog's  sciatic  nerve  gave  responses  homodrome  with  ex- 
citation, larger  on  the  anodic  than  on  the  kathodic  side.  But  a 
detailed  examination  of  blaze-currents  in  nerve  and  in  muscle 
still  remains  to  be  made. 


REFERENCES 

Du  Bois-Reymond.  —  "  Ueber  secundar-elektromotorische  Erscheinungen 
an  Muskeln  Nerven  und  elektrischen  Organen,"  Sitzungsberichte  Berlin^ 
5th  April  1883,  p.  343  ;  and  du  Bois-Reymond'' s  Archiv,  p.  i,  1884. 

Du  Bois-Reymond. — "  Lebende  Zitterochen  zu  Berlin,"  du  Bois-Reymond^ s 
Archiv,  p.  86,  1885. 

Hering.  —  "  Ueber  du  Bois-Reymond's  Untersuchung  der  secundar- 
elektromotorischen  Erscheinungen  am  Muskel,"  Wiefter  Sitzungs- 
be7'ichte,  22nd  November  1884,  p.  445   (and  p.  415). 

Hermann. — "  Ueber  Sogenannte  secundar-elektromotorische  Erscheinun- 
gen an  Muskeln  und  Nerven,"  Pfiiiger's  Archiv,  xxxiii.,  p.  103,  1884. 

GOTCH. — "  The  Electromotive  Properties  of  the  Electrical  Organ  of  Torpedo 
Marmorata,"  Phil.  Trans.  Roy.  Soc,  p.  487,  1887,  and  p.  329,  1888. 

Burdon-Sanderson  and  Gotch. — "On  the  Electrical  Organ  of  the 
Skdite."  Journal  of  Physiology,  vol.  9,  p.  137,  1888  ;  vol.  10,  p.  259,  1889. 

ROEBER.  —  "  Ueber  das  Elektromotorische  Verhalten  der  Froschhant  bei 
Reizung  ihrer  Nerven,"  du  Bois-Reymo7ids  Archiv,  p.  633,  1869. 

Engelmann. — "  Die  Hautdriisen  des  Frosches,"  PJlUger's  Archiv,  vi.,  p.  97, 
1872  (also  vols,  iv.,  p.  I,  321,  and  vol.  v.,  p.  498). 

Hermann. — "  Ueber  die  Secretionsstrome  und  die  Secretreaction  der  Haut 
bei  Froschen,"  Pfiiiger's  Archiv,  xvii.,  p.  291,  1878. 

Bach  u.  Oehler  [Hermann]. — Pfiiiger's  Archiv,  xxii.,  p.  30,  1880. 

Bayliss  and  Bradford. — "  On  the  Electrical  Phenomena  accompanying 
Secretion  in  the  Skin  of  the  Yxo%"  Journal  of  Physiology,  vol.  7,  p.  217, 
1886. 

Reid. — "  The  Electro-motive  Properties  of  the  Skin  of  the  Common  Eel," 
Phil.  Trajts.  Roy.  Soc,  p.  335,  1893. 

Reid  and  Tolput. — "  Further  Observations  on  the  Electromotive  Proper- 
ties of  the  Skin  of  the  Common  Eel,"  Jour?ial  of  Physiology,  vol.  16, 
p.  203,  1894. 

Waller. — "  On  Skin-currentg  ;  The  Frog's  Skin,"  Proc.  Roy.  Soc,  vol.  68, 
p.  480,  1 90 1. 


LECTURE  VI 

A  Representative  Experiment — Effects  of  Indirect  Excitation — Effects  of 
Direct  Excitation  immediately  after  Death,  and  Later — How  Long, 
after  a  Cat's  Death,  can  a  Cat's  Foot  continue  to  Exhibit  Signs  of 
Life  ? — More  A  B  C — A  Vegetable  Surface — Surface  against  Surface 
— Anodic  and  Kathodic — Biedermann  and  the  Frog's  Tongue — A 
Warnino-. 


§  6 1.  Demonstration. — This  cat  is  dead,  but  its  tissues  are 
still  alive.  It  was  decapitated  at  4.45  ;  it  is  now  5.5,  and  I  shall 
talk  with  my  eye  on  the  clock,  as  I  wish  to  show  you  an  experi- 
ment just  half  an  hour  after  the  death  of  the  cat. 


Fig.  41. — Diagram  of  experiment  described  in  the  text. 

The  story  of  the  cat's  skin,  or,  more  properly  speaking,  of  its 
foot-pad,  commences  from  the  observations  of  Hermann  and 
Luchsinger,  who  showed  that  on  the  skin,  as  on  glands,  secreto- 
motor  can  be  disentangled  from  vasomotor  reactions.  The 
experiment  of  Hermann  and  Luchsinger  cannot  be  shown  here. 
It  is  a  vivisection  of  which  preliminary  No.  i  is  the  abolition  of 

G 


58  THE  SIGNS  OF  LIFE  [lect. 

muscular  movement  by  curare,  and  therefore  preliminary  No.  2 
is  artificial  respiration. 

It  is  now  5.10  P.M.;  the  cat  has  been  dead  twenty-five 
minutes.  I  have  therefore  five  minutes  time  to  further  explain 
my  meaning.  The  surviving  tissues  are  dying  ;  the  junction 
between  motor  nerve  fibre  and  muscular  fibre  is  dying  ;  the 
junction  between  secretomotor  fibre  and  gland  cell  is  also 
dying ;  but,  according  to  my  experience,  the  first  will  die  in 
thirty,  the  second  will  die  in  sixty  minutes.  I  have  therefore 
a  margin  of  thirty  minutes  during  which  excitation  of  that 
packet  of  nerve  fibres  called  the  sciatic  nerve  will  not  cause  any 
movement  of  the  limb  (nor,  therefore,  any  possible  shifting  of 
contacts  or  other  disturbance),  but  will  cause  an  activity  of  the 
cutaneous  glands.* 

You  will  find  as  a  book  datum  (and  as  a  printed  datum  it  is 
a  very  satisfying  datum)  that  the  independence  of  secretomotor 
nerves  is  proved  by  the  fact  that  after  death  (of  the  cat),  when 
the  circulation,  and  therefore  vasomotor,  effects  are  out  of  count, 
beads  of  sweat  are  made  to  appear  on  the  carefully  wiped  pad 
by  excitation  of  the  sciatic  nerve. 

I  have  never  succeeded  in  witnessing  these  beads  of  sweat, 
and  will  not  therefore  make  the  attempt  to  demonstrate  them 
to  you ;  but  I  shall  show  you  by  means  of  the  galvanometer, 
within  this  margin  between  the  thirtieth  and  sixtieth  minute 
post-mortem,  that  the  excitation  of  the  sciatic  nerve  on  one  side 
(and  on  the  other),  causes  a  marked  physical  alteration  in  the 
skin  of  the  pad,  first  on  one  side  and  then  on  the  other.  Cats 
differ,  and  I  will  not  answer  for  my  times  to  a  minute,  but  it 
is  now  thirty-five  minutes  post  mortem  felis,  and  I  am  well  within 
the  margin.  The  two  hind  pads  are  connected  with  the  two 
terminals  of  the  galvanometer,  I  don't  know  which  is  which,  so 
I  test  my  connections  with  a  bit  of  zinc,  by  touching  the 
two  terminals  on  the  operation  table  with  which  the  two 
galvanometer  terminals  are  connected.  Touching  the  terminal 
of  the  left  pad  with  the  bit  of  zinc,  while  my  finger  is  on  the 

*  The  longest  period  recorded  in  my  notes  has  been  2  hrs.  15  mins.,  in 
the  case  of  a  particularly  well-nourished  cat. 


VI.]  '       SECRETO-MOTOR  EFFECTS  99 

terminal  connected  with  tlie  right  pad,  sends  the  spot  off  to 
your  right ;  I  know,  therefore,  that  on  excitation  of  the  left  sciatic, 
the  spot  will  go  to  your  right.  I  know  that  the  skin  under  its 
control  is  rendered  zincative  (galvanometrically  negative  accord- 
ing to  physiologists,  electro-positive  according  to  physicists — but 
in  any  case  in  the  direction  of  the  arrow  on  the  black  board — 
from  outer  to  inner  surface  of  that  skin,  z>.,  in  an  ingoing 
direction). 

The  spot  has  "flown  off  scale" — as  Biedermann  so  often 
expresses  it — to  your  right  (I  am  giving  a.  demonstration,  and 
not  making  a  measurement).  In  order  to  save  time  to  make 
the  converse  experiment  without  undue  delay,  I  bring  the  spot 
back  by  the  counter  current  of  a  compensator.  I  have  used 
.015  volt;  that  therefore  has  been  the  approximate  electro- 
motive value  of  the  response — by  no  means  an  inconsider- 
able value. 

I  now  apply  similar  excitation  to  the  sciatic  nerve  of  the 
right  side.  You  think  nothing  happens,  but  before  you  have 
made  up  your  mind  that  nothing  happens,  the  spot  flies  off  to 
the  left.  Opposite  side — opposite  direction  of  course.  Ingoing 
current  in  the  right  side  gives  deflection  to  the  left,  just  as 
ingoing  current  in  the  left  side  gave  deflection  to  the  right ;  and 
the  pause  perceptible  to  most  of  you  at  the  second  observation, 
but  not  at  the  first,  was  the  latent  period  between  cause  and 
effect,  between  excitation  of  the  sciatic  nerve  and  response  of 
the  cutaneous  gland-cell.  I  guess  it  to  be  about  three  seconds, 
but  we  will  measure  it  presently. 

This  obvious  delay  between  excitation  and  response  should 
make  its  mark  upon  your  memory.  It  is  a  sure  and  reassuring 
sign  that  we  are  dealing  with  a  true  physiological  response, 
outside  all  possibility  of  coarse  physical  fallacy.  The  response 
— I  mean  the  indirect  response  of  the  skin  to  excitation  of  the 
nerve — can  be  elicited  by  a  single  induction  .shock.  This  in 
itself  is  rather  curious  ;  we  should  have  expected  a  visceral 
(sudo-motor)  nerve  to  need  prolonged  or  summating  stimuli 
for  its  effective  excitation ;  you  see  for  yourselves,  however, 
that  a  single  shock  causes  an  unmistakably  delayed,  well- 
marked  and  somewhat  prolonged  response. 


100  THE  SIGNS  OF  LIFE  [lect. 

The  nerve-skin  response,  now  before  your  eyes,  is  a  very 
good  case  to  use  for  familiarising  you  with  some  of  our 
apparatus. 

We  guessed  the  lost  time  at  three  seconds,  we  will  now  make 
a  rather  more  accurate  measurement  by  photographing  a  galvano- 
metric  deflection,  and  finally  we  will  control  our  measurement 
by  taking  an  electrometer  photograph.     (  Vide  infra,  p.  105.) 

Two  galvanometers  are  in  circuit  in  series  (as  described 
in  the  Appendix,  p.  1 56);  the  recording  galvanometer  or  galvano- 
graph  will  take  on  the  sensitive  plate  a  replica  of  the  indica- 
tion witnessed  by  you  on  the  demonstrating  galvanometer,  and 
it  will  be  rather  interesting  to  you,  perhaps,  to  see  whether 
the  impression  on  your  mind  is  borne  out  by  the  impression 
on  the  photographic  plate.  The  plate  is  set  to  fall  at  the 
rate  of  about  2.5  mm.  per  second  (or  an  inch  in  10  seconds), 
and  the  instant  of  stimulation  is  signalled  on  the  plate  by 
a  device  that  you  can  examine  afterwards.  I  start  the  clock- 
work, and  2  or  3  seconds  after  you  have  heard  the  commence- 
ment of  excitation  (of  the  nerve),  you  see  the  deflection 
caused  by  the  electrical  change  that  has  taken  place  in  the 
skin.  When  the  plate  has  got  to  the  end — i.e.,  after  40  seconds 
— it  is  shut  up  in  its  carrier  and  sent  to  the  developing-room, 
from  which  it  will  be  brought  back  in  a  few  minutes,  and 
placed  in  the  projecting  lantern  (Fig.  43). 

Meanwhile  let  us  examine  the  response  by  means  of  another 
instrument — the  capillary  electrometer — put  into  the  circuit 
instead  of  the  galvanometers  (Appendix,  p.  162).  The 
magnified  image  (x  about  1500  diameters)  of  the  mercury 
column,  projected  on  the  transparent  screen,  looks  to  you  like 
a  large  manometer — and,  in  point  of  fact,  it  is  an  electrical 
manometer,  as  you  see  at  once  if  I  raise  or  lower  the  elec- 
trical pressure  in  circuit  by,  e.g.,  thousandths  of  a  volt 
Having  verified  that  the  connections  are  such  that  movement 
of  the  mercury  upwards  on  the  screen  signifies  outgoing 
current,  and  downwards  the  reverse,  we  may  proceed  to  excite 
the  sciatic  nerve  as  before  and  watch  the  electrometer  image 
on  the  screen.  It  reacts  perfectly  well — by  a  downward  move- 
ment  each   time   I   excite  the  sciatic  nerve — and  my  impulse 


VI.]  DIRECT  EXCITATION  101 

is  to  exclaim  on  seeing  these  responses  on  the  screen — "  What  a 
splendid  cat !  "  For  they  are,  as  you  may  have  noticed,  responses 
to  single  break  induction  shocks.  And  notice  also  the  delay, 
about  2  seconds — with  an  electrometer  this  time.*  But  we  must 
photograph  this,  which  will  be  easily  and  expeditiously  done  on 
the  lecture-table  by  slipping  in  a  recording  instrument,  so  as  to 
receive  the  image  of  the  mercury  column.  This  is  now  done  ; 
the  plate  travels  horizontally  at  a  rate  of  about  3  mm.  per 
second ;  the  record  is  completed  in  40  seconds,  and  in  a  few 
minutes  you  will  be  able  to  compare  it  with  that  previously 
taken  by  the  recording  galvanometer,  and  with  your  own 
memory-image  (Fig.  44). 

I  repeat  the  two  experiments  to  make  sure  that  the  effects 
of  indirect  excitation  are  clear  to  you,  and  turn  to  the  results 
of  direct  excitation.  I  have  no  history  to  give  you  in  this 
connection,  nor  list  of  German  names.  You  must  be  satisfied 
with  the  story  of  the  thing  as  given  by  the  thing  itself — not  a 
complete  story  indeed,  but  a  fragment,  a  word  or  two. 

§  62.  Direct  excitation.  —  A  pad  of  the  cat's  foot  is  cut  off 
and  placed  between  electrodes  on  a  bit  of  ebonite  with  a 
central  perforation,  to  ensure  normal  passage  of  the  excita- 
tion current.  Excitation,  compensation,  etc.,  are  applied  as 
you  now  well  understand  from  previous  lectures,  in  accordance 
with  the  diagram  now  fully  familiar  to  you  (p.  152).  I  compensate 
exactly,  so  that  the  galvanometer  may  be  plugged  and  un- 
plugged without  disturbance  (notice  in  passing  that  the  current 
to  be  compensated  has  been  from  surface  to  section,  i.e.,  ingoing 
through  the  skin  ;  it  cannot  therefore  be  current  of  injury,  for 
such  current  should  be  from  section  to  surface,  i.e.,  outgoing 
through  the  skin)  ;  I  excite  the  pad  by  a  break  induc- 
tion shock  in  the  ingoing  direction,  and    on    unplugging   the 

*  In  another  case  a  series  of  electrometer  records  came  out : — 
Time  post  mortem    .         ,     30     40     48      55      65     minutes. 
Voltage  of  response  .         .     12      10       8        5        2      millivolts. 
Period  of  latency       .         .     1.4     1.6     1.7     1.8     2.0     seconds. 
There  was  no  appreciable  lost  time  with  direct  excitation,  nor    exces- 
sive delay   of  transmission    in  the  nerve  itself ;  the  delay  was  exclusively 
"junctional," 


102  THE  SIGNS  OF  LIFE  [lect. 

galvanometer  you  see  an  effect  (or  after-effect)  in  that  same 
direction.  I  turn  over  the  reverser  of  the  exciting  current,  I 
apply  a  similar  induction  shock  in  the  outgoing  direction  ;  the 
response  (or  after-affect)  as  you  see,  is  again  to  your  left,  in  the 
ingoing  direction,  and  it  is  larger  than  the  previous  one ;  there 
is  perhaps  a  polarisation  factor  (ingoing  after  outgoing)  that 
makes  this  ingoing  response  larger  than  in  the  previous  case, 
where  the  polarisation  factor  (outgoing  after  ingoing)  was 
opposite  to  the  main  physiological  ingoing  effect — but  that  is  a. 
detail.  The  principal  point  is,  that  the  effects  of  electrical 
excitation  of  whatever  direction  have  been  ingoing,  or  as  I 
choose  to  call  it — "  negative." 

The  effects  of  excitation  in  either  direction  being  ingoing,  it 
is  clear  that  a  series  of  currents  of  alternating  directions  will 
produce  an  ingoing  effect.  Tetanisation,  i.e.^  a  series  of  make- 
and-break  current  in  rapid  succession,  will  therefore  produce  an 
ingoing  effect ;  and  as  you  now  see,  that  ingoing  effect  is  off 
scale  to  your  left ;  there  has  been  a  summation  of  separate 
stimuli  forming  the  tetanising  series. 

I  reverse  the  direction  of  the  tetanising  currents,  and  as 
before,  you  see  the  spot  flying  off  scale  to  your  left,  indicating 
response  (or  more  precisely  after-effect)  through  the  directly 
excited  pad  in  the  ingoing  direction. 

This  has  been  a  single  experiment.  I  do  not  remember 
having  ever  seen  better  marked  ingoing  effects  of  excitation  ; 
but  the  pad  was  very  fresh,  and  I  did  not  use  very  strong 
tetanisation,  which  two  conditions  have  been  shown  by  previous 
experiments  to  be  favourable  as  regards  the  demonstration  of 
ingoing  effects  of  direct  excitation.  In  previous  experiments  I 
have  indeed  observed  precisely  the  reverse  effects,  viz.,  outgoing 
effects  by  direct  excitation  ;  but  I  was  then  following  out  the 
effects  day  by  day,  and  using  excitation  of  full  strength,  in 
order  to  learn  how  long  after  the  death  of  a  cat  this  sign  of  life 
was  observable  on  one  of  its  feet. 

Such  a  pad  has  now  been  set  up,  taken  from  a  cat  twenty- 
four  hours  after  death,  and  you  see  as  a  matter  of  fact  that  it 
gives  large  outgoing  effects  (deflections  to  your  right)  after  both 
directions  of  strong  tetanisation. 


VI.] 


OUTGOING  EFFECTS 


103 


It  is  an  easy  matter  in  the  case  of  an  animal  like  the  cat, 
to  test  the  skin  in  situ.  Two  or  three  hours  after  death,  when 
the  muscles  are  no  longer  inconveniently  excitable,  a  pad  is 
cut  off,  and  one  electrode  is  applied  to  the  wounded  surface  ; 
the  other  electrode  is  applied  to  an  intact  pad.     The  accidental 


Fig.  42.  (4219.) — Outgoing  responses  of  the  pad  of  a  cat's  foot,  directly  excited 
by  single  break  induction  shocks  in  both  directions,  and  by  tetanising  currents  in 
both  pairs  of  directions. 

current  (which  is  not  an  "  injury  current,"  since  its  direction  in  the 
cat  is  from  intact  to  injured  spot,  but  the  normal  and  accidental 
ingoing  current  at  the  uninjured  spot)  is  compensated,  and  the 
blaze  test  applied  in  the  usual  way.  Both  responses  are  in 
the  same  direction  as  that  of  the  accidental  current,  from  intact 
to  wounded  spot,  ingoing  through  the  intact  skin.  These 
are  evidently  not  negative  variations  of  any  injury  current. 

We  may  provisionally  infer  from  the  absence  of  obvious 
injury  current  that  the  subcutaneous  connective  tissue  is  of 
very    inert    character,    and    that    an    unpolarisable    electrode 


104  THE  SIGNS  OF  LIFE  [lect. 

applied  to  subcutaneous  tissue  will  serve  us  as  an  indifferent 
electrode,  under  which  little  or  no  local  response  to  excita- 
tion need  be  expected.  But  we  must  take  care  that  the 
wound  does  not  involve  injured  or  exposed  muscle,  we  need 
only  transfer  our  "  indifferent "  electrode  to  an  injured  muscle 
(or  to  an  injured  nerve)  to  be  convinced  that  the  latter  is 
strongly  electromotive  in  the  usual  (zincative)  sense.  The 
hint  may,  perhaps,  prove  of  some  service  to  us ;  we  may  one 
day  want  to  make  use  of  an  indifferent  electrode  for  the 
further  investigation  of  the  electrical  reactions  of  undisturbed 
skin  or  mucous  membrane.  Reflect  for  an  instant — we  must 
always  get  a  resultant  of  two  factors,  if  our  circuit  includes 
two  active  surfaces,  whether  both  be  of  skin,  or  both  mucous 
or  one  skin  and  one  mucous.  So  that  to  get  at  the  reaction 
of  one  spot  of  skin  in  situ  or  of  mucosa  in  situ,  it  will  greatly 
simplify  our  task  if  the  subcutaneous  tissue  may  be  treated 
as  electrically  indifferent  and  non-responsive. 

§  63.  Review. — We  have  gone  over  the  whole  ground,  and 
rather  more  rapidly  than  I  expected.  These  three  experi- 
ments— exhibiting,  first,  the  ingoing  current  aroused  by  in- 
direct excitation ;  second,  the  ingoing  current  aroused  by  not 
too  strong  direct  excitation  of  a  fresh  pad  ;  third,  the  outgoing 
current  aroused  by  strong  direct  excitation  of  a  twenty-four 
hour  pad — very  fairly  summarise  all  I  have  learned  about  these 
currents  during  the  last  few  months.  Some  few  details  may, 
indeed,  be  added — the  lost  time  of  indirect  excitation  for  instance, 
and  the  rapid  exhaustion  of  the  indirect  effect  by  repeated 
stimuli ;  but  these  will  be  best  shown  to  you  by  projecting  On 
the  screen  the  actual  records  of  these  phenomena.  And  I  may 
mention  that  in  one  experiment  directed  to  the  point,  it  was 
found  that  no  effect  was  produced  by  excitation  post-mortem 
of  the  sciatic  nerve  of  a  previously  atropinised  cat,  and  that  in 
another  experiment  the  same  state  was  found  on  a  cat  killed 
by  chloroform  *  ;  in  both  these  experiments  the  effects  of  direct 
excitation  were  found  to  be  normal.     One  other  point — in  both 

*  In  other  cats,  chloroformed  and  killed,  the  indirect  effects  have  always 
t?een  normal ;  the  instance  (quoted  in  the  text  was  exceptional. 


VI.] 


THE  LATENT  PERIOD 


105 


excised  pads  that  we  tested  by  direct  excitation,  the  "normal 
current "  was  ingoing — in  precisely  the  opposite  direction  to 
what  might  have  been  expected  in  a  piece  of  living  tissue  with 
an  artificial  section — in  one  pad  the  effects  of  excitation  were 
ingoing,  increments  of  the  normal  current ;  in  the  other  they 
were  outgoing,  decrements  of  the  "  normal  current." 

Seconds. 


•DOS 
voLC 

Fig  43. — Cat.  Ingoing  response  of  pad  of  foot  aroused  by  excitation  of  the 
sciatic  nerve.  Berne  coil  at  1000  units.  The  latent  period  is  3  seconds.  (Galvano- 
meter record.) 

Here  are  the  records  you  saw  taken  a  few  minutes  ago 
(p.  100),  showing  the  lost  time  and  the  course  of  the  indirect 
effect,  on  the  galvanometer  and  on  the  electrometer.     Compar- 

Seconds. 

H   I   I    I   I   I   I    I   I 


Fig.  44. — Electrometer-record.     Indirect  response  (ingoing)  of  cat's  foot-pad  to 
single  break  induction  shock  through  sciatic  nerve.     Lost  time  =  3  seconds. 

ing  the  two  curves,  you  see  that  they  have  very  similar  time- 
relations,  and  there  does  not  seem  to  be  much  to  choose  between 
the  two  instruments.     This,  however,  is  merely  due  to  the  fact 


106 


THE  SIGNS  OF  LIFE 


[lect. 


that  the  phenomenon  is  comparatively  slow  and  prolonged,  so 
that  it  can  be  followed  and  observed  by  galvanometer  almost 
as  well  as  by  electrometer  ;  the  former  instrument  has  indeed 
inertia  and  "  lost  time,"  but  these  are  not  considerable  in  com- 
parison with  the  physiological  inertia  and  lost  time  of  the  change 
observed  ;  this  particular  galvanometer  has  a  lost  time  of  about 
0.3  second,  z>.,  only  one-tenth  that  of  the  physiological  lost  time 
under  observation ;  the  electrometer  has  no  appreciable  lost 
time,  which  of  course,  is  an  advantage. 

The  voltage  of  the  response  is  greater  in  the  galvano- 
metric  than  in  the  electrometric  curve,  but  that  is  only 
incidental  to  the  fact  that  in  the  former  case  the  response 
was  taken  to  tetanisation,  and  in  the  latter  to  a  single 
induction  shock ;  perhaps  also  the  nerve-skin  was  becoming 
fatigued.  Such  fatigue,  in  consequence  of  repeated  action, 
does  in  fact  always  appear  in  more  or  less  pronounced  degree. 
Here  is  an  instance  in  which  it  is  very  well  marked. 

The  direct  (blaze)  effects 
that  persist  for  hours  or 
days  after  the  indirect  ex- 
citability of  the  skin  and 
the  indirect  and  direct  ex- 
citability of  muscle  have  dis- 
appeared. I  am  here  refer- 
ring to  the  direct  and  indirect 
excitability  of  muscle  in  the 
usual  acceptation  of  these 
terms ;  I  have  not  yet 
studied  in  detail  the  direct 
(blaze)  effects  in  either 
muscle  or  nerve,  but  only 
in  the  skin.  The  question, 
"  How  long  does  a  cat's  foot 
live  ? "  is,  I  believe,  to  be 
answered  by  reference  to  the  blaze-currents  of  the  skin,  which 
I  have  found  in  a  favourable  case  as  long  as  a  week  post- 
mortem, when  no  other  sign  of  life  on  any  other  tissue  could 
be  detected.     And    by   a  favourable   case    I    mean    that   of  a 


o  5  mins. 

Fig.  45. — Cat.  Response  of  skin  to 
tetanisation  of  the  sciatic  nerve,  repeated  at 
I  minute  intervals,  and  lasting  for  about  5 
seconds.  The  deflections  at  the  beginning  and 
at  the  end  of  the  record  are  standardising  de- 
flections by  xoirth  volt. 


VI.] 


ABC 


107 


strong,  well-nourished  cat — the  half-starved  derelicts  that  some- 
times find  their  way  into  a  physiological  laboratory  have  a  dead 
skin  two  or  three  days  post-mortem. 

§  64.  More  A  B  C. — Our  second  half-hour  will  have  been 
well  employed  if  the  application  of  what  in  the  last  lecture  was 
entitled  the  ABC  method  can  be  made  absolutely  plain.  We 
shall  follow  the  system  of  notation  that  I  then  recommended  to 
your  attention,  and  work  through  the  four  tests  on  a  cat's  foot  in 
accordance  with  the  following  diagram,  which  gives  the  ABC 
switch  in  its  several  positions  and  the  manner  of  its  connection 


t:o  the 
keyboard. 


bo  Che 
keyboard. 


Switch 


Skin 


Excitation  from  B  to  A  (B  is  anodic) 

Response  outgoing  at  B 
Excitation  from  A  to  B  (B  is  kathodic) 

Response  outgoing  at  B 
Excitation  from  B  to  A  (A  is  kathodic)  ■ -v 

Response  outgoing  at  A  ' *" 

Excitation  from  A  to  B  (A  is  anodic)  < ^ 

Response  outgoing  at  A  ^ 

Fig.  46. — -Cat's  paw  (24  hours  post-mortem),  A,  B,  C,  as  indicated  above.  Ex- 
citation by  tetanising  currents.  Berne  coil.  Two  Leclanches.  10,000  units.  The 
response  is  always  of  the  nature  of  an  outgoing  current  at  A,  and  at  B  for  both  direc- 
tions of  excitation. 

with  the  keyboard  and  galvanometer.  You  will  see,  if  you  trace 
out  the  connections,  that,  with  the  switch  in  the  first  position, 
deflection  to  your  right  means  current  from  B  to  A,  that  in  the 
position  IP  it  means  current  from  B  to  C,  and  that  in  the  posi- 
tion 11^  it  means  current  from  C  to  A.  By  a  glance  at  the 
switch  and  reverser,  you  can  therefore  recognise  the  direction  of 
excitation  and  the  direction  of  response  at  B  or  at  A  ;  and  it 
will  be  a  perfectly  simple  matter  to  work  through  the  four  tests 


108  THE  SIGNS  OF  LIFE  [lect. 

to  verify  the  following  formula,  which  previous  experiments  have 
shown  to  be  that  of  the  responses  of  a  cat's  paw  twenty-four 
hours  after  death  : — 


B 


Excitation  from  B  to  A  (B  is  anodic) 

Response  outgoing  at  B  *■     " 

Excitation  from  A  to  B  (B  is  kathodic)  < 

Response  outgoing  at  B  < 

Excitation  from  B  to  A  (A  is  kathodic)  >. 

Response  outgoing  at  A  i^— ^ 

Excitation  from  A  to  B  (A  is  anodic)  < 

Response  outgoing  at  A  * 

And  now,  if  I  have  succeeded  in  making  clear  to  you  that  the 
deflections  seen  on  the  scale  indicate  current  in  the  object 
towards  B  {i.e.,  out  at  B),  or  towards  A  (out  at  A),  or  from  B  (in 
at  B),  or  from  A  (in  at  A) — the  results  of  the  experiment  will  be 
clear  to  you  as  it  progresses. 

I  intend  to  examine  B  ;  I  therefore  compensate  the  points 
B  C  with  the  switch  in  the  position  II  .  Then  I  plug  the 
galvanometer  at  the  keyboard,  move  the  switch  to  the  first 
position,  and  send  a  break  induction  shock  through  the  paw 
from  B  to  A.  I  turn  back  the  switch  to  the  old  position,  IP, 
and  unplug  the  galvanometer.  The  deflection  is  to  your  left 
as  figured,  signifying  that  there  is  now  current  from  C  to  B  (the 
previous  anode),  which  is  outgoing  at  B.  It  is  what  in  Bieder- 
mann's  terminology  is  called  a  negative  anodic  current — i.e., 
"  negative  "  to  the  original  current. 

I  repeat  a  second  trial  in  precisely  the  same  way,  but  with  a 
reversed  direction  of  excitation,  so  that  B  is  now  its  kathode. 
The  deflection  is  again  to  your  left,  outgoing  at  B  ;  it  is  a  posi- 
tive, kathodic  current — i.e.,  "  positive  "  to  the  original  current. 

And  in  precisely  the  same  way,  as  a  confirmatory  pair  of 
trials,  I  repeat  on  the  A  C  side ;  only,  perhaps,  especially  if  the 
previous  trials  have  been  made  with  strong  currents,  it  may 
be  prudent  to  shift  the  electrode  A  to  a  fresh  pad.  Both  the 
trials  give  deflection  to  your  right,  outgoing  at  A,  positive 
kathodic  after  excitation  from  B  to  A,  negative  anodic  after 
excitation  from  A  to  B.  So  that  the  formula  previously 
sketched  has  been  precisely  fulfilled  ;  all  the  responses  have 
been  outgoing. 


VI.]  .  VEGETABLE  "SKIN"  109 

§  65.  A  vegetable  surface. — In  contrast  with  the  preceding, 
let  me  now  show  you  another  group  of  four  trials — on  a  vegetable 
surface — of  which  the  formula  has  been  drawn  up  beforehand,  to 
be  verified  presently.     I  have  chosen  a  geranium  leaf 

But  let  us  pause  a  moment  to  reflect  upon  the  conditions  of 
experiment  if  we  were  limited  to  the  use  of  two  electrodes,  and 
had  no  previous  knowledge  of  the  direction  in  which  the  re- 
sponse takes  place.  We  should  be  obliged  to  apply  our  elec- 
trodes to  two  external  points  of  the  leaf,  the  deflection  would  be 
the  sum  or  the  difference  between  two  opposed  responses,  and 
we  could  not  tell  which  was  the  greater  of  the  two.  Suppose, 
e.g.,  that  we  applied  the  two  electrodes  to  opposite  points  on 
the  upper  and  lower  surfaces,  and  observed  a  response  directed 
from    upper   to   lower   surface  ;    this  might  result  either  from 


two  outgoing  currents      A 
that    at   B    exceeding    ^ 
that  at  A  :  B 


or  from  two  ingoing  ^ 
currents,  that  at  A  — t- 
exceeding  that  at  B  :      B 


and  until  we  know  whether  the  effects  are  ingoing  or  outgoing, 
we  could  not  decide  between  the  two  alternatives.  We  are 
obliged  to  use  three  electrodes  to  enable  us  to  test  separately 
the  point  A  and  the  point  B,  by  connecting  first  one  and  then 
the  other  point  through  the  galvanometer  with  an  indifferent 
point  C. 

We  proceed  then  with  the  experiment,         B         C         A 
having  clearly  realised  the   simplicity  and        j  ;j  *" 

necessity    of    its    apparent    complication.  ^ 

The  results,  as  you  see,  come  out  precisely       2"'""  '"'"^ 

as  figured  in  the  diagram  before  you :  > 

All   four    reactions   are    ingoing ;  Nos. 
I    and    4    are    homodrome    post-anodic ;  <  4 

Nos.  2  and  3  are  antidrome  post-kathodic. 

§  66.  Surface  against  surface. — x'\nd  now,  having  learned 
that  the  reactions  of  the  external  surface  of  a  leaf  are  ingoing, 
we  may  make  use  of  the  resultant  effect  when  only  two  elec- 
trodes are  used,  to  learn  whether  one  of  two  points  or  of  two 
surfaces  acts  more  powerfully  than  the  other.  Is,  e.g.,  the 
ingoing  blaze  of  the  upper  or  of  the  lower  surface  predominant 


110  THE  SIGNS  OF  LIFE  [lect. 

when  points  of  both  surfaces  act  against  each  other  through  the 
galvanometer?  If  to  both  directions  of  excitation,  the  resultant 
is  in  one,  say,  a  descending  direction,  we  may  be  pretty  sure 
that  the  upper  surface  reacts  more  powerfully  than  the  lower 
surface ;  but  to  make  quite  sure,  it  is  better  to  take  two  pairs  of 
tests,  reversing  the  order  of  direction  in  each  pair,  i.e.,  to  take 
the  responses  after  excitations  B  to  A,  A  to  B,  and  after  excita- 
tions A  to  B  then  B  to  A,  because  it  may  well  happen  with 
excitations  of  any  considerable  strength  that  the  first  is  greater 
than  a  second  excitation,  and  we  are  not  assured  that  a  differ- 
ence thus  caused  might  not  disturb  a  comparison. 

Homodrome  post-anodic  of  upper  surface  greater  than 

Antidrome  post-kathodic  of  lower  surface  ;  therefore  ^      I         | 

Homodrome  descending  response  A  to  B.  ZIUXX3-jZ 

B—j— ^ !_£_ 

Antidrome  post-kathodic  of  upper  surface  greater  than  -'. 

Homodrome  post-anodic  of  lower  surface  ;  therefore  ^        ^ 

Antidrome  descending  response  A  to  B. 

A  result  of  this  character  clearly  proves  that  the  blaze  of 
the  upper  surface  of  a  leaf  (beside  geranium  I  have  also  tested 
lilac  and  violet  leaves)  predominates  over  the  blaze  of  its  lower 
surface.  The  ingoing  current  of  the  upper  surface,  whether 
anodic  or  kathodic,  has  exceeded  the  ingoing  current  of  the 
lower  surface,  whether  kathodic  or  anodic.  We  must  be  careful, 
however,  to  secure  equal  arese  of  the  two  exciting  electrodes  (see 
§69). 

§  6^.  Anodic  versus  Kathodic  blase. — You  ask  again,  whether, 
ccsteris  paribus,  an  anodic  or  a  kathodic  blaze  is  the  greater. 

To   answer  this   question,  you   only 
require  to  make  a  sufficient  number 

of  trials    in  which  the  two  currents 

^       ^    *  are  opposed  to  each  other  from  points 

E^c.  ^  on  one  surface.     You  apply,  e.g.,  your 

^^'  two  electrodes  to  the  upper  surface 

(or  to  the   lower   surface),   and    find 

that  the  after-effect  is  homodrome  with  the  exciting  current. 

You  conclude  that  normally  the  post-anodic  ingoing  homodrome 

blaze  exceeds  the  post-kathodic  ingoing  antidrome  blaze. 


VI.]  THE  FROG'S  TONGUE  111 

The  frog's  skin  gives — with  two  electrodes  applied  to  its 
external  surface — a  similar  positive  effect ;  but  in  this  instance 
we  found,  by  analysing  its  polar  factors,  that  the  after-effect  is 
homodrome  with  the  exciting  current  by  reason  of  an  excess 
of  post-kathodic  outgoing  homodrome  over  post-anodic  out- 
going antidrome  blaze.  The  complete  formulae  in  the  two  cases 
run  as  follows  : — 


Eccc 


Fruit  skim  □         ,^^^^,,    ^ 
or  Leaf.   \Resp.(t:otaL)   ^ 


'> 


Eacc. 
Frog  skin\  Resp  (bo cab) 
Resp.  (parCiaL)' 


I  68.  Tongue  surfaces. — The  frog's  tongue,  examined  in 
the  usual  way  by  the  electrodes  applied  to  the  upper  and 
lower  surfaces,  presents  an  analogous  case  to  that  of  a  leaf; 
its  response,  when  stimulated,  is  the  resultant  of  two  effects 
at  the  two  opposite  poles.  The  tongue,  as  it  lies  on  the  floor 
of  the  mouth,  gives  an  ascending  resultant,  which,  if  we  might 
be  sure  that  the  effects  were  outgoing  at  the  two  surfaces, 
indicates  that  the  upper  surface  of  the  tongue  acts  more  power- 
fully than  the  lower  surface.  The  current  of  rest  is  descending, 
and  if  we  may  admit  as  proved  that  the  upper  is  the  more  effec- 
tive surface,  this  descending  resultant  indicates  an  ingoing 
current  of  rest. 

But  the  detailed  study  of  the  frog's  tongue  belongs  to  the 
intricate  and  theoretically  important  subject  of  mucous  currents, 
which  has  been  treated  of  at  a  considerable  length  by  Bieder- 
mann.  I  hope  to  discuss  the  whole  question  of  mucous  currents 
in  a  more  complete  manner  than  is  possible  to-day.  Any  one 
who  is  curious  in  the  matter  should  refer  to  Biedermann's  papers 
or  to  the  full  account  in  his  Electro-physiology.  You  will  find 
there  that  he  attributes  great  importance  to  the  positive  and 
negative  responses  of  the  tongue  in  connection  with  the  theory 
of  assimilatory  and  dissimilatory  phenomena.     You  may  very 


112 


THE  SIGNS  OF   LIFE 


[lecT. 


probably  think,  as  I  do,  that  an  organ  with  two  effective 
epitheHal  layers,  even  if  one  of  these  layers  is  greatly  more 
effective  than  the  other,  is  not  the  most  suitable  object  to 
afford  contrary  electrical  effects  significant  of  contrary  chemical 
changes.  It  would  have  been  preferable  if  Biedermann  had 
based  his  case  upon  contrary  electrical  effects  of  a  single 
mucous  surface.  And  I  think  that  when  you  have  reflected 
upon  the  conditions  of  the  problem,  you  will  realise  as  a 
clear  economy  of  labour  and  an  escape  from  much  perplexity, 
to  methodically  follow  the  ABC  plan  for  the  separate  examina- 
tion of  the  single  points  A  and  B  of  a  simple  mucous  surface. 
I  have  done  so  to  some  extent,  but  by  no  means  sufficiently. 
As  far  as  I  have  gone,  I  find  that  the  electrical  response  of  a 
mucous  surface  may  be  ingoing  or  outgoing,  but  that  it  is 
usually  the  former.  Here,  e.g.^  is  the  record  of  a  series  of 
ingoing  responses  of  a  frog's  stomach : — 


1/iAW— ir 


l§      Eccc.  &i    BLaze    ingoing. 


SeroscL 


Fig.  47.— Frog.  Stomach.  Two  series  of  ingoing  responses  to  ingoing  single 
break  induction  shocks  at  one  minute  intervals.  Interval  of  one  hour  between  the 
first  and  second  series. 


I  69.  A  warning. — Let  me  here  put  you  on  your  guard 
against  a  fallacy  to  which  I  was  myself  hardly  alive  in  the 
first  comparisons  of  anode  versus  kathode,  and  surface  against 
surface.  It  is  important  that  the  area  of  contact  between 
surface  and  electrode  shall,  as  far  as  possible,  be  equal  on 
both  sides  and  not  accidentally  extended  by  excess  of  clay  or 
by  fluid  used  to  moisten  the  electrodes.     As  a  matter  of  fact,  it 


VI.] 


CURRENT-DENSITY 


113 


generally  happened  that  this  necessary  condition  obtained  in 
my  earliest  experiments,  for  the  tubes  of  both  electrodes  were 
of  equal  bore,  and  any  excess  of  fluid  around  them  was  removed 
by  filter  paper.  But  failing 
this  precaution,  we  should  be 
liable  to  have  unequal  effects, 
due  to  unequal  current  densi- 
ties at  the  two  poles.  If  the 
inequality  is  very  marked,  we 
shall  obtain  greater  response  — 
from  the  pole  of  smaller  area 
{i.e.,  where  current  density  is 
greater),  whether  that  pole  be 
anode  or  kathode.  The  fact 
deserves  to  be  illustrated  by  an 
experiment  ad  hoc.     Here  then 


Fro.  48. 


is  a  living  surface — it  happens  to  be  a  vegetable  surface — to 
which  two  electrodes  of  different  area  are  applied ;  the  exci- 
tation is  applied  first  in  one  then  in  the  other  direction,  and 
as  you  see,  both  the  responses  are  in  the  same  direction, 
ingoing  at  the  pointed  electrode,  whether  that  electrode  has 
been  anodic  or  kathodic. 

Will  some  one  be  good  enough  to  repeat  this  experiment 
on  a  piece  of  frog's  skin  ?  I  should  expect  him  to  find  both 
responses  to  be  outgoing  at  the  pointed  electrode,  instead  of 
ingoing  as  in  the  vegetable  surface.* 

*  This  has  since  been  verified  by  Dr  Alcock. 


REFERENCES 

Hermann  u.  Luchsinger. — "Ueber  die  Secretionsstrome  der  Haut  bei 

der  Katze,"  P finger's  Archiv,  xvii.,  p.  310,  1878. 
Waller. — "  On  Skin-currents.     Observations   on    Cats,"  Proc.  Roy.   Soc, 

vol.  69,  p.  171,  1901. 
Biedermann. — "Ueber  Zellstrome"   (Frog's   Tongue),   Pfliiger's  Archiv, 

liv.,  p.  209,  1893. 
BOHLEN  (Biedermann). — "Ueber  die  elektromotorischen  Wirkungen  rde 

Magenschleimhaut,"  P finger's  Archiv,  Ivii.,  p.  97,  1894. 
Biedermann. — "  Elektrophysiologie,"  Jena,  1895  (translated  by  Miss  F.  A. 

Welby.     Macmillan  &  Co.,  1896-98). 

H 


LECTURE  VII 

Observations  on  the  Human  Skin — Du  Bois-Reymond's  Experiments — 
Tarchanoffs  Observations — Sweat-prints — Introduction  of  Ions  through 
the  Skin. 

Experiments  by  which  electro-motive  reactions  are  sought  to 
be  demonstrated  on  the  human  subject  are  full  of  pitfalls,  and 
beset  with  fallacies.  I  do  not  consider  that  any  one  of  the  three 
principal  experiments  I  am  about  to  show  you  ought  to  be  re- 
garded as  convincing  or  conclusive,  and  it  is  mainly  as  an  exercise 
in  criticism  that  they  have  been  prepared  for  demonstration, 

A  monotonous  series  of  successful  experiments  is  against  all 
nature ;  lecture-table  discoveries  are  never  as  easy  as  they  are 
made  to  appear  ;  there  is  often  more  real  instruction  in  "  failure  " 
than  in  "  success." 

§  70.  A  fruitless  "  expei'iment."  —  More  than  one  person, 
on  learning  that  a  blaze-current  is  a  characteristic  sign  of  life, 
has  said  this  :  "  Will  my  finger  give  a  blaze-current  if  I  place 
it  between  those  electrodes  :  it  is  alive  I  suppose  ?  "  To  which 
question  the  obvious  reply  is,  "  Try  it."  In  some  cases  the 
"student"  has  said,  "Oh,  I  don't  like  electric  shocks,"  and  his 
research  has  terminated  at  this  point.  But  if  of  a  more  inquir- 
ing type,  he  has  perhaps  placed  a  finger  between  the  electrodes, 
and  thereby  experienced  a  first  difficulty  in  this  simple-looking 
experiment.  He  cannot  keep  his  finger  absolutely  still  between 
the  electrodes,  and  the  galvanometer  spot  wanders  aimlessly 
to  and  fro  on  the  scale.  The  "  research "  may  stop  here  ;  the 
"student"  has  to  catch  a  train;  his  scientific  curiosity  is  satis- 
fied. A  third  student  having  cleared  the  first  (imaginary)  and 
second  very  real  and  most  obstructive  fence,  keeps  his  finger  fairly 
quiet  between  the  electrodes,  so  that  it  is  possible  to  neutral- 
ise the  accidental  effects  occurring  between  electrodes  and  skin, 
and  get  the  galvanometer  spot  fairly  steady  at  or  near  its  zero 
point.     An  induction  shock  may  now   be  passed  through  the 

114 


LECT.  vii.]  THE  HUMAN  SKIN  115 

finger.  This  is  the  third  fence ;  for  take  the  shock  as  weak  as 
you  like,  and  you  may  be  sure  that  the  patient  will  jump,  shift 
contact,  disturb  compensation,  and  have  to  begin  over  again 
many  times,  before  he  is  able  to  keep  his  finger  quiet  while  a 
sufficiently  strong  shock  is  passed  through  it.  But  let  us  say 
that  he  has  reached  this  point,  and  that  his  finger  is  in  circuit, 
steady  and  currentless,  and  unmoved  when  a  shock  is  passed. 
You  would  find,  even  now,  that  the  response  is  uncertain, 
irregular,  and  capricious,  always  open  to  the  objection  that 
contact  between  skin  and  electrodes  has  been  altered  during 
experiment.  And  if  you  reflect  upon  the  conditions  of 
experiment,  I  think  you  may  fairly  abandon  it  at  this  point. 
For  you  have  at  best  the  resultant  of  two  opposite  effects  at 
the  two  electrodes,  which  resultant  will  depend  upon  at  least  two 
or  three  unknown  variables.  You  do  not  know  what  is  the  normal 
direction  of  skin  response,  nor  whether  one  or  other  portion  of 
skin  is  physiologically  more  or  less  effective,  nor  whether  there  are 
polar  differences  when  one  or  other  portion  is  anodic  or  kathodic. 
The  original  question  cannot  be  answered  by  this  apparently  simple, 
but  in  reality  most  objectionable  and  complicated  experiment. 

I  am  not  sure  yet,  in  spite  of  several  trials  of  the  point, 
whether  or  no  a  conclusive  answer  is  to  be  obtained  as  to  the 
nature  and  direction  of  excitatory  currents  in  the  intact  human 
skin.  I  am,  however,  quite  sure  that  no. such  answer  is  to  be 
got  with  a  single  pair  of  electrodes,  and  that  we  must  first  study 
the  separate  polar  effects  by  the  ABC  method,  B  C  A 

exciting  through  A  B,  leading  off  through  A  C    ^        *" 

or  B  C  after  previous  compensation. 

I    did   this   two   years  ago,  obtaining  what  <  ■         g 

then  appeared  to  me  to  be  sufficiently  constant  ^ >• 

and  regular  effects  ;  the  formula  of  skin  response 

was  thus —  >  4 

The  responses  Nos.  i  and  4,  being  antidrome  to  the  exciting 
current,  I  regarded  as  equivocal ;  Nos.  2  and  3,  being  homodrome 
to  the  exciting  current,  as  unequivocal.  All  the  responses 
were  "  ingoing  "  at  the  excited  spot,  a  direction  that  is  gener- 
ally assumed  to  be  the  normal  direction  of  skin-current  in  the 
cat  and  in    man.     But   there  was   the  principal  and    unavoid- 


116  THE  SIGNS  OF  LIFE  [lect. 

able  defect  in  these  trials,  that  they  have  not  and  cannot  be 
repeated  on  the  same  skin  after  death  ;  so  that  we  cannot  feel 
certain  that  the  so-called  unequivocal  responses  have  not  been 
due  to  anomalous  polarisation,  which  with  the  form  of  elec- 
trodes employed  was  found  liable  to  occur.  Amalgamated  zinc 
plates  covered  with  chaniois  leather  soaked  in  zinc  sulphate 
are  rarely  free  of  polarisation  currents,  ordinary  kathodic 
antidrome  as  well  as  anomalous  anodic  homodrome,  and  with 
tetanisation  they  give  a  formula  in  all  points  similar  to  that 
given  above.  I  do  not  therefore  regard  the  results  as  being 
conclusive  until  repeated  with  more  perfect  electrodes. 

The    fallacy  caused    by  anomalous 
mca.ke    ^         C      A     polarisation  of  imperfect  electrodes — so 


brcdLk  1 >      far  from  being  avoided  by  the  use  of 

',|^  }    tetanising  currents — is  favoured,  for  we 

nnd.He  i •>■      then  have  to  do  with  antidrome  katho- 

^^'^      '*  ^  ^    die    polarisation  by   one  current  plus 

<  /    homodrome  anodic  polarisation  by  the 

opposite  current. 

§  71.  A  fruitful  experiment. — Allusion  has  been  made  above 
to  the  "blaze-currents"  of  excised  human  skin  (§  53,  p.  86),  and 
I  should  like  to  bring  the  point  once  more  under  your  notice,  as 
it  has  been  for  the  last  few  weeks  under  my  close  observation, 
I  wanted  to  know  how  long  after  death  this  sign  of  life  can  be 
detected  in  the  skin  itself,  and  whether  the  duration  of  survival 
is  found  to  vary  after  various  modes  of  death.  The  skin  is  a 
tissue  of  quite  remarkable  vitality  ;  it  seems  as  if  it  had  learned 
to  resist  injury  from  its  surroundings,  and  to  have  become  tough 
and  hardy  of  habit.  You  may  have  noticed  in  your  rambles  logs 
by  the  wayside  from  which  young  shoots  have  sprung  from 
surviving  subcortical  tissues ;  perhaps  you  have  heard  that  on 
Napoleon  I.'s  removal  from  St  Helena  to  the  Invalides,  his  toe- 
nails were  found  to  have  grown  through  his  boots — a  sign  of  the 
extraordinary  vitality  of  the  cells  of  the  nail-matrix,  or  of  the 
perishable  quality  of  boot-leather  —  nearly  twenty  years  had 
elapsed  between  burial  and  exhumation.  There  is  no  doubt 
whatever  that  the  hair  grows  after  death. 


Vll.] 


DIRECT  EFFECTS 


117 


In  surgical  practice  it  is  a  very  common  proceeding  to 
accelerate  the  recovering  of  a  raw  surface  by  "skin-grafting." 
It  is  essential  that  such  grafts  should  include  cells  of  the 
malpighian  layer. 

All  these  things  point  to  an  exceptional  vitality  of  cutan- 
eous or  rather  subcutaneous  malpighian  elements. 

I  find  that  in  the  skin  of  persons  dying  suddenly  in  other- 
wise good  health,  the  cutaneous  blaze-currents  persist  for  several 
days,  whereas  the  skin  taken  from  ordinary  post-mortem  room 
subjects,  having  died  gradually  and  completely,  exhibits  little 
or  none  of  this  sign  of  life  twenty-four  and  forty-eight  hours 
post  mortem. 

Let  me  remind  you  of  the  nature  of  this  sign,  for  the 
questions  to  which  it  may  serve  as  an  indicator  are  by  no  means 
exhausted.  A  piece  of  living  skin  set  up  between  electrodes, 
and  tested  in  the  usual  way  by  induction  currents  of  both 
directions,  responds  by  blaze-current  in  one  —  the  outgoing 
direction.  A  piece  of  dead  skin  does  nothing  of  the  kind,  but 
gives,  if  anything,  small  polarisation  counter-currents.  And 
since  living  skin  responds  in  one  direction  to  both  directions 
of  excitation,  you  may  (observing  due  reservation  and  pre- 
caution) obtain  outgoing  blaze-currents  after  tetanisation  by 
alternating  currents  in  both  pairs  of  directions.  Here  are 
galvanometric  records  of  the  electrical  responses  of  surviving 
human  skin,  and  of  the  same  skin,  killed  by  heat. 


vote 
o-oos 


Living: 


c-ooio 
voLb. 


TTTITTT 

Dead. 


Fig.  49  (4201).— Skin  of  breast  8  hours  after  amputation.  Living. — Two  + 
responses  to  single  break  induction  shocks  in  +  and  -  directions.  8  L.  10,000. 
Bead. — Several  -  and  +  effects  to  +  and  -  shocks,  ?>.,  polarisation.  Resistance 
diminished. 


118 


THE  SIGNS  OF  LIFE 


EOmin. 

Fig.  50  (^Nos.  4199-4200). — Skin  of  breast  5  hours  after  amputation.  Tested  \>y 
tetanising  currents  for  periods  of  5  seconds  each  from  a  Berne  coil  at  5000  units, 
supplied  by  8  Leclanche  cells.  Conductance  at  outset  of  experiment  ==  5,  and 
calculated  resistance  =  320,000  ohms.  After  tetanisation  the  conductance  was 
raised  to  12.5  (=  196,000  ohms);  after  further  tetanisation  it  rose  further  to  25 
(^88,000  ohms),  when  the  record  commenced.  The  resistance  of  the  galvanometer 
and  electrodes  -  20,000  ohms.      The  deflection  by  ^Vth  volt  through  i  megohm  =  27. 

A^  living.- 


h\  boiled.- 


-Conductance  at  outsel 

=  25 

1st  response  to  tetan., 

ra. 

-, 

br. 

-1- 

—   +0.0120  volt. 

2nd         ,,              ,,  ' 

m. 

-t-, 

br. 

-, 

=   +0.0092      ,, 

3rd         „ 

m. 

-, 

br. 

+  , 

=  +0.0100     ,, 

4th 

m. 

-f , 

br. 

-, 

=  +0.0076     „ 

Conductance  at  end 

=  35 

-Conductance        .     . 

-  115 

1st  response  to  tetan., 

m. 

- 

br. 

+  , 

=  +0.0004  volt. 

2nd         ,,              „ 

m. 

+ 

br. 

-, 

=   -0.0004    11 

3rd 

m. 

- 

br. 

-f 

~  +0.0004    „ 

4th          „              „ 

m. 

+ 

br. 

- 

-  -0.0004    )> 

Conductance   .     .     . 

. 

. 

.     . 

. 

=  US 

.] 


THE  CONGELATION  BLAZE 


119 


One  more  point  to  conclude  this  matter  of  the  surviving 
human  skin.  If  a  piece  of  Hving  skin,  placed  between  electrodes 
and  connected  with  a  galvanometer  in  the  usual  way,  is 
gradually  cooled  in  a  freezing- 
box,  we  shall  notice,  at  a 
given  temperature  of  about 
-  5°,  a  sudden  deflection  of  the 
galvanometric  spot  indicative 
of  a  sudden  electromotive 
change.  The  effect  is  due  to 
the  sudden  congelation  of  the 
under-cooled  tissue.  This 
"  congelation  blaze,"  which  is 
manifested  by  vegetable  as 
well  as  by  animal  tissues,  is  in 
general  their  last  sign  of  life  ; 
if  the  frozen  tissue  is  thawed, 
and  then  cooled  a  second 
time,  there  is  little  or  no 
second  blaze  according  as  the 
tissue  has  been  more  or  less 
completely  killed  by  the  first 
proceeding.  In  the  present 
case,  that  of  the  human  skin, 
the  congelation  blaze-current 
is  of  outgoing  direction. 

Alterations  of  electrical  resistance  occur  in  marked  degree  in 
connection  with  the  electromotive  effects  that  first  attract  our 
attention.  Surviving  skin  as  it  dies  exhibits  a  fall  of  resistance. 
There  is  a  well-marked  diminution  of  resistance  as  the  im- 
mediate consequence  of  electrical  excitation ;  Fig.  50  incident- 
ally shows  this.  And  in  the  course  of  cooling,  there  is  first  a 
gradually  increasing  resistance,  then  at  the  point  of  congelation 
a  sudden  increase  of  resistance,  which  in  some  instances  is 
preceded  by  a  small  and  evanescent  diminution,  not  unlike  a 
congelation  blaze,  which,  however,  I  have  reason  to  attribute  to  a 
slight  rise  of  temperature  and  of  conductivity  occurring  when 
the  under-cooled  tissue  juices  pass  from  the  liquid  to  the  solid 


o  5  10  m  ins. 

Fig.  51  (4209). — Skin  of  man.  2nd 
day  after  excision.  Skin  gradually  cooled 
by  surrounding  the  skin-chamber  with  a 
freezing  mixture.  Sudden  electromotive 
discharge  (outgo'ng  current)  at  a  tempera- 
ture of  -  6°  inside  the  skin-chamber.  Be- 
fore freezing  the  +  responses  to  +  and  - 
single  induction  shocks  were  +0.004  ^nd 
+  0.008  volt.  After  freezing,  the  +  responses 
were  absent,  being  replaced  by  small  — 
and  +  polarisation  effects.  On  recongela- 
tion  no  second  discharge  was  observed. 


120  THE  SIGNS  OF  LIFE  [lect. 

state.  But  the  details  of  this  effect  require  closer  investigation 
than  I  have  yet  found  time  to  give  to  them.  Thawed  skin, 
subsequent  to  congelation,  has  a  greatly  diminished  resistance 
— e.g.,  a  diminution  to  50,000  ohms  from  an  original  resistance 
of  1 50,000  ohms. 

Vegetable  tissues  likewise  exhibit  a  very  marked  diminution 
of  resistance  in  consequence  of  excitation,  and  the  diminution 
is  not  solely  a  diminution  of  "  contact  resistance "  at  the  elec- 
trodes. It  is  internal  or  interpolar  as  well,  owing  probably 
to  a  multiplication  of  electrolytes,  possibly  also  to  an  actual 
rupture  of  cell  membranes.  A  very  simple  experiment  will 
serve  to  show  you  that  the  augmented  conductivity  is  inter- 
polar as  well  as  polar.  A  flower  stalk  is  laid  across  four 
unpolarisable  electrodes,  E  I  I  E,  at  5  cm.  intervals  ;  a  tenth 
of  a  volt  is  allowed  to  act  upon  the  galvanometer  through  the 
entire  length  of  stalk  E  E,  and  through  an  intermediate  portion 
I  I.  The  deflections  indicate  the  current  strength,  and  there- 
fore the  conductance  of  the  corresponding  lengths  of  stem. 
Noting  their  values  before  and  after  tetanisation  of  the  whole 
stem  through  the  terminal  electrodes  E  E,  you  will  find  that 
the  conductance  is  augmented  in  the  intermediate  part  I  I, 
showing  that  the  alteration  is  not  restricted  to  the  contacts  E  E. 
The  conductance  of  I  I,  which  was  0.8  y  before  the  excitation 
through  E  E,  is  raised  to  2.0  y ;  in  E  E  itself,  it  has  been  raised 
from  0.4  y  to  1.6  y.* 

§  72.  Du  Bois  experiinent.  —  The  galvanometer  is  in  its 
usual  position,  with  its  magnets  pointing  N  and  S,  and  the 
scale  correspondingly  arranged  N  and  S  ;  you  may  consider  that 
the  two  ends  of  the  scale  represent  the  two  terminals  of  the 
galvanometer,     I  am  seated  facing  you  below  the  scale,  with'my 

*  The  symbol  7  denotes  our  unit  of  conductivity.    (See  Appendix,  p.  169.) 
The  conductance  and  resistance  in  the  above  experiment  are  : — 


of  I  I  before 

0.8  7 

1.25    fi, 

after 

2.0,, 

0-5      „ 

E  E  before 

0.4,, 

2.5      » 

after 

1.6  „ 

0.625  „ 

Vll.] 


DU  BOIS'  EXPERIMENT 


121 


left  hand  connected  with  the  S  terminal,  and  my  right  hand 
with  the  N.  The  forefinger  of  each  hand  dips  in  salt  solution, 
there  is  little  or  no  difference  of  potential  between  my  two 
hands,  and  the  spot  is  at  rest. 


Fig.  52. — Du  Bois-Reymond's  "Willkiirversuch,"  to  demonstrate  a  negative 
variation  during  voluntary  muscular  contraction.  The  current  is  ascending  in 
the  active  arm.     (From  du  Bois-Reymond's   Thierisclie  Elektrtcitat). 

I  now  firmly  contract  the  muscles  of  my  right  forearm  ; 
the  spot  moves  to  my  right  (your  left),  or  clockwise  in  the 
circuit,  or  in  my  body  from  right  to  left.     The  spot  is  "  pulled." 

Now  I  contract  the  muscles  of  my  left  forearm,  and  every- 
thing is   reversed.      You   have  witnessed   du  '  Bois-Reymond's 


122  THE  SIGNS  OF  LIFE  [lect. 

celebrated  "  willkiirversuch,"  by  which  he  considered  that  he 
had  demonstrated  on  the  normal  human  subject  the  electrical 
effects  of  voluntary  muscular  contraction,  and  I  think  you  may 
be  interested  to  see  the  actual  figure  by  which  he  illustrated 
the  experiment  (Fig.   52). 

The  usual  criticism  quoted  of  this  experiment  is  that  of 
Hermann,  who  explains  the  deflection  observed  in  du  Bois- 
Reymond's  experiment  as  being  the  effect  of  a  secretion  current 
provoked  in  the  skin  of  the  contracting  side.  He  says  that 
in  the  skin  of  that  side  such  current  will  be  directed  from 
without  inwards,  giving  current  ascending  in  the  active  arm. 

This  criticism  is  based  upon  observations  by  Hermann 
and  Luchsinger  concerning  the  effects  of  atropine  on  the 
sweat  currents  of  cats,  and  he  expresses  himself  as  follows : — 
"  A  curarised  man  could  give  the  du  Bois  current  in  the 
absence  of  muscular  contraction.  In  the  case  of  an  atropinised 
man  it  would  be  absent,  in  spite  of  the  presence  of  muscular 
contraction."  *" 

I  do  not  myself  think  that  the  alternative  explanation  is 
necessary.  To  my  mind,  du  Bois-Reymond's  experiment  does 
not  demonstrate  the  existence  of  contraction  currents  on  man  ; 
nor  do  Hermann's  experiments  on  cats  show  that  du  Bois' 
currents  on  man  are  secretion  currents.  Neither  the  contraction 
current  nor  the  secretion  current  has  been  separately  obtained 
on  man  ;  the  currents  that  we  have  witnessed  are  susceptible 
of  a  far  simpler  explanation. 

I  think  they  are  simply  capillary  currents  arising  at  the 
surface  of  separation  between  salt  solution  and  skin.  Let  me 
show  you  a  couple  of  experiments  in  point. 

Instead  of  dipping  the  two  fingers  simultaneously,  I  will  dip 
them  successively,  so  that  the  skin  of  one  finger  may  be  pretty 
completely  soaked  when  the  skin  of  the  second  finger  com- 
mences to  be  moistened.  There  is  no  deflection  so  long  as 
only  one  finger  is  introduced,  but  on  introduction  of  the  second 
finger  there  is  current  through  the  galvanometer  from  the  first 
to  the  second  finger,  therefore  through  the  body  from  the  second 

*  Hermann,  Handbuch,  vol.  i.,  p.  225. 


vir.]  TAtlCHANOFF'S  EXPERIMENT  123 

to   the   first.      The   spot   is   "  pulled   by  the  ingoing  capillary 
soakage." 

Here,  now,  is  a  counter  experiment : — 

Both  fingers  are  resting  against  the  bottom  of  the  vessels,  as 
indeed  was  recommended  by  du  Bois-Reymond  in  order  to 
avoid  the  fallacy  that  I  have  just  mentioned,  and  when  the  spot 
is  at  rest  I  squeeze  one  of  my  fingers,  say,  of  the  left  hand, 
against  the  bottom  of  the  vessel.  The  current  through  the 
galvanometer  is  now  from  the  compressed  skin.  The  spot  is 
"pushed."  In  case  you  should  object  to  the  possible  muscular 
or  secretory  origin  of  the  current  by  reason  of  the  voluntary 
action  on  that  side  used  to  effect  the  compression,  I  will  remain 
perfectly  passive,  and  have  the  compression  effected  by  a  second 
person  without  any  act  of  mine.  The  effect  follows  as 
before. 

While  I  am  on  this  subject,  let  me  show  you  one  more 
surface  experiment.  You  have  seen  that  contraction  pulls  the 
spot,  that  soaking  skin  pulls  the  spot,  that  squeezed  skin  pushes. 
I  want  to  dry  a  wet  finger  in  order  to  dip  it  in  dry,  I  naturally 
rub  it,  and  then  proceed  to  show  that  on  soaking  it  again  the 
spot  is  pulled.  But  now,  as  you  see,  the  effect  is  reversed,  the 
spot  is  pushed  ;  dry  rubbed  skin  pushes  the  spot. 

And  so  we  may  use  for  our  memorandum,  that  if  zinc 
pulls  the  spot,  last-dipped  and  therefore  soaking  skin  pulls, 
that  squeezed  skin  pushes,  and  that  recently  rubbed  skin 
pushes.  Neither  du  Bois-Reymond's  contraction  current,  nor 
Hermann's  secretion  current  are  above  suspicion  in  presence 
of  those  unavoidable  capillary  currents.  And  for  my  part  I 
find  it  quite  impossible  to  contract  the  muscles  of  my  forearm 
without  moving  a  finger  or  pressing  it  against  something. 

§  73.  Tarchanoff's  experimejit.  —  Over  ten  years  ago,  Tar- 
chanoff  published  an  account  of  observations  on  the  skin- 
currents  of  the  human  subject,  in  which  he  considered  that  he 
had  obtained  evidence  of  their  reflex  causation  by  all  kinds 
of  peripheral  stimuli — by  tickling,  by  induction  shocks,  by 
pricking  with  a  pin,  by  hot  and  cold  water,  by  sudden  sound, 
sight,  taste,  and  smell.     He  assures  us,  further,  that  imaginary 


124  THE  SIGNS  OF  LIFE  [lec-t. 

sensations,  intellectual  effort,  or  strained  attention  bring  about 
similar  effects — "always,  of  course,  during  complete  immobility 
of  the  subject."  Voluntary  movement  of  any  part  of  the  body, 
during  absolute  quiescence  of  the  part  connected  with  the 
galvanometer,  gives  a  skin  current  the  strength  of  which  is 
dependent  on  the  strength  of  the  voluntary  effort.  He  says 
that  parts  in  which  sweat-glands  are  most  abundant  (palm  of 
hand,  toes,  axilla,  etc.)  become  negative  to  parts  containing  few 
glands  (back,  nates,  external  surface  of  thigh  and  arm),  and 
considers,  therefore,  that  the  active  state  of  the  nervous  system 
gives  rise  to  an  ingoing  secretion  current  similar  to  that  shown 
by  Hermann  in  the  case  of  the  frog's  skin,  by  excitation  of  its 
cutaneous  nerves. 

Tarchanoff  further  assures  us  that  he  used  a  sensitive,  almost 
completely  aperiodic,  galvanometer,  giving  with  the  nerve  cur- 
rent of  a  frog's  sciatic  a  deflection  "  off  scale  "  {i.e.,  greater  than 
50  divisions) ;  the  skin  effects  he  observed  also  gave  deflections 
"  off  scale,"  had  a  latent  period  of  one  to  three  seconds,  outlasted 
the  stimulus  by  several  minutes,  and  returned  gradually  but 
irregularly  to  rest.  Connection  with  the  skin  was  made  from 
unpolarisable  electrodes  of  th-e  usual  type  by  strips  of  hygro- 
scopic wool  (10  to  15  cm.  long)  soaked  in  normal  saline,  brought 
in  contact  with  pads  of  the  same  material  previously  applied  to 
the  skin.  These  pads  were  of  an  area  of  10  to  15  cm.  The 
currents  of  rest  were  previously  compensated.  In  the  case  of 
the  hand,  the  effect  of  gentle  tickling  was  generally  such 
that  "die  Basis  der  Finger  in  der  Mehrzahl  der  Falle  nega- 
tive, der  Thenar  dagegen  positive  elektrische  Spannung 
besitzt."  Imaginary  sensation  gave  deflections  of  10  to  15 
divisions. 

Now  these  things  are  clearly  of  considerable  interest,  if  a 
true  physiological  effect  regularly  coincident  with  nervous 
activity  can  be  demonstrated  ;  and  I  have  somewhat  minutely 
described  to  you  the  conditions  of  observation,  in  case  any  one 
should  be  inclined  to  make  fair  and  patient  test  of  the  state- 
ments. I  must  confess,  however,  that  for  my  own  part  I  am  not 
convinced  that  the  deflections  have  been  anything  more  than 
rather   unduly    pronounced    galvanometric    vagaries    occurring 


VII.]  IMPORTATION  OF  IONS  125 

with  shifting  contacts.  We  all  know  how  difficult  it  is  to  pre- 
serve a  limb  absolutely  quiet,  and  that  even  when  we  think  that 
our  muscles  are  completely  at  rest,  a  "thought-reader"  can 
obtain  information  from  our  unconscious  movements.  It  is  no 
easy  matter  to  have  a  loose  pad  immobile  against  the  skin,  and 
if  it  be  fixed  by  a  band,  the  least  swelling  or  movement  will  alter 
its  pressure  against  the  skin  ;  and  I  cannot  say  that  I  have  suc- 
ceeded in  satisfying  myself  that  the  irregular  deflections  that 
certainly  do  occur  with  a  subject  keeping  as  quiet  as  possible, 
and  more  markedly  when  the  subject  is  anywise  startled  or 
stimulated,  have  been  anything  else  than  the  effects  of  accidents 
of  surface  contact.  I  am  willing  to  admit  that  they  might  be 
accidents  of  nervous  tension  giving  true  alterations  of  skin- 
currents,  but  I  cannot  admit  that  this  possibility  has  been 
proved  to  the  exclusion  of  the  coarser  fallacy.  Will  any  one 
undertake  to  clear  up  this  point?  If  so,  perhaps  it  may  be 
worth  while  to  mention  that  the  skin  can  be  locally  atropinised  * 
by  means  of  a  belladonna  plaster,  and  that  obviously  a  locally 
atropinised  skin  should  show  no  effect  of  glandular  action,  but 
the  usual  effects  of  accidents  of  contact. 

I  do  not  think  that  these  observations  on  the  human  sub- 
ject are  particularly  satisfactory,  and  shall  not  dwell  upon  them 
any  longer.  I  will  use  the  remainder  of  the  hour  to  place 
before  you  certain  facts  relating  to  the  transport  of  medica- 
ments into  the  human  body  under  the  influence  of  the  galvanic 
current. 

§  74.  Importation  of  ions. — All  such  facts  are  illustrations  of 
the  principles  of  electrolytic  conduction.  If  a  sufficiently  strong 
current  is  passed  through  a  saline  solution,  or,  as  I  am  about  to 
show  you,  through  a  porous  electrode  soaked  in  a  saline  solution, 
the  electro-positive  kations  of  the  salt  travel  with  the  current 
from  the  anode  to  the  kathode,  while  the  electro-negative 
anions  travel  against  the  current  from  the  kathode  to  the  anode. 
Taking,  e.g..,  the  case  of  NaCl,  the  Na  travels  with  the  current, 
the  CI  against  the  current.     You  may  for  the  present  purpose 

*  Aubert,  "Sweat-prints,"  Anfi.  de  Dertnatologie,  1877-8;  Article 
"  Sueur,"  (by  Francois  Franc)  in  Diet.  Encycl.  des  Scienqes^  Medicales.,  xiii. 


126 


THE  SIGNS  OF  LIFE 


[lect 


regard  the  tissues  as  represented  by  a  sponge  of  such  NaCl 
solution  ;  if  you  pass  the  current  into  the  body  by  porous 
electrodes  soaked  in  some  other  salt — and  for  this  purpose  we 
shall  take  permanganate  of  potash — ^you  will,  after  a  few  minutes, 
observe  a  visible  sign  of  the  transfer  of  the  anion  from  electrode 
to  body  in  the  form  of  a  discoloration  of  the  skin  at  the  spot 
where  the  anions  have  travelled  against  the  direction  of  current 
from    kathode   to    anode.      I    chose   permanganate   of   potash 


K 


MnO> 


Fig.  53. — Circular  areae  of  skin  of  the  forearm  that  have  served  as  electrodes  to  a 
constant  current  for  a  few  minutes.  In  the  upper  pair  of  circles  the  two  electrodes  in 
contact  with  the  skin  were  a  solution  of  permanganate  of  potash  ;  the  coloured  ion  was 
the  anion  Mn04,  which  travels  up  stream  and  enters  the  body  at  the  kathode.  In  the 
lower  pair  of  circles,  the  two  electrodes  in  contact  with  the  skin  were  a  solution  of 
copper  sulphate  ;  the  coloured  ion  was  the  kation  Cu,  which  travels  down  stream  and 
enters  the  body  at  the  anode. 


because  it  has  a  coloured  ion,  in  this  case  the  anion.  If  I  had 
taken  copper  sulphate,  where  it  is  the  kation  copper  that  is 
coloured,  I  should  have  made  the  anodic  spot  the  more  apparent 
since  the  metal  travels  with  the  current  and  is  carried  into  the 
body  at  the  anode. 

Two  electrodes — one-inch  glass  tubes  half  full  of  perman- 
ganate of  potash— are  strapped  to  the  front  of  my  forearm, 


VII.]  AN  OBITER  FACTUM  127 

and  perpendicular  to  it.  The  electrodes  are  connected  with 
the  house  current,  which  is  at  no  volts.  Out  of  caution  for  my 
own  comfort,  I  have  means  of  taking  any  desired  fraction  of  the 
whole  current ;  and  to  tell  what  current  I  am  taking,  there  is  a 
milliamperemeter  in  circuit  with  my  arm.  The  electrodes  have 
arese  of  about  seven  square  centimetres,  and  a  current  of  between 
two  and  three  milliamperes  should  produce  a  distinct  result  in 
about  five  minutes.  The  kathode  is,  I  believe,  nearer  to  the 
wrist,  the  anode  above  it ;  but  we  shall  soon  see,  for  it  is  at  the 
kathode  that  we  shall  find  evidence  of  penetration  of  the  coloured 
anion,  MnO^. 

The  trial  is  over ;  and  after  washing  the  forearm  under  the 
tap,  you  see  a  number  of  indelible  brown  spots  over  the  pre- 
viously kathodic  area  of  the  skin,  which  are  due  to  its  penetra- 
tion by  the  coloured  anion,  which  you  remember  travels  against 
the  current,  and  therefore  gets  into  the  body  where  the  current 
leaves  it.  Notice  their  clearly  defined  punctiform  appearance  ; 
this  signifies  that  the  path  of  current  has  been  chiefly,  if  not 
entirely,  by  way  of  the  sweat-ducts,  hardly  or  not  at  all  through 
the  general  epidermic  investment. 

A  similar  principle  of  transport  holds  good  in  the  case 
of  other  electrolytes,  and  it  is  interesting  to  note,  in  the 
case  of  poisonous  salts,  whether  it  is  the  anode  or  the 
kathode  that  acts  as  the  channel  of  introduction.  In  most 
cases,  e.g.,  in  that  of  strychnine  sulphate,  the  poisonous 
property  belongs  to  the  base,  the  kation,  which  penetrates  at 
the  anode  ;  in  others,  e.g.,  in  that  of  cyanide  of  potassium,  it 
belongs  to  the  acidic  moiety,  the  anion,  which  penetrates  by  the 
kathode.  In  the  first  case  the  anode  is  the  poison  carrier,  the 
kathode  being  innocuous  ;  in  the  second  case  it  is  the  kathode 
that  kills.  If,  following  the  example  of  Leduc,  I  should  place 
two  rabbits  side  by  side,  connecting  them  by  a  couple  of  elec- 
trodes of  indifferent  nature,  i.e.,  soaked  in  NaCl,  and  then 
run  a  current  through  both  rabbits  in  series,  by  means  of  elec- 
trodes moistened  with  strychnine  sulphate,  I  should  put  the 
anodic  rabbit  into  strychnine  convulsions  by  reason  of  pene- 
tration of  the  kation,  while  the  kathodic  rabbit,  taking  in  only 
the  non-toxic  anion,  would  remain  quite  unaffected. 


128  THE  SIGNS  OF    LIFE  [lect.  vn. 

§  75.  A  supplementary  experiment. — Let  us  take  advantage, 
of  the  altered  area  of  skin  of  our  KMn04  experiment  to  make 
a  further  trial.  Its  sweat-ducts  are  choked  with  Mn04 — i.e.,  with 
a  non-living  electrolyte  that  may  serve  us  as  a  conductor  to 
the  inner  aspect  of  the  skin.  I  should  like  to  take  this  altered 
area  of  skin  and  an  unaltered  area  of  intact  skin  into  circuit 
with  an  induction  coil  and  a  galvanometer,  to  be  tested  in  the 
usual  way.  This  is  now  done  by  tubes  of  zinc  sulphate,  and  the 
first  point  you  notice  is  that  there  is  a  considerable  current 
directed  in  the  body  from  the  irritated  to  the  intact  spot,  or 
ingoing  through  the  former  and  outgoing  through  the  latter. 
This  current  being  compensated  and  the  galvanometer  plugged 
out,  I  apply  excitation  in  the  usual  way  by  induction  shocks  and 
by  tetanisation,  and  look  for  the  after-currents  that  may  be 
aroused.  In  accordance  with  your  expectation,  they  are  in 
every  case  opposed  to  the  current  of  injury — i.e.,  ingoing  at  the 
intact  skin  and  outgoing  at  the  manganised  skin.  This  result, 
as  far  as  it  goes,  agrees  with  the  conclusion  that  the  normal 
irritated  skin  of  man  is  the  seat  of  an  ingoing  current ;  but  I 
should  be  sorry  to  lay  much  stress  on  the  result  of  an  isolated 
experiment,  the  point  deserves  further  investigation. 


REFERENCES 


Du    Bois-Reymond. — "Willkiirversuch,"   Untersiichttngeti  iteber  thierische 

Elektricitdf,  vol.  ii.,  p.  289,  1849. 
Hermann. — "Ueber  den  Actionsstrom  der  Muskeln  im  lebenden    Men- 

schen,"  Pfliigei^s  Archiv,  xvi.,  p.  410,  1878. 
Tarchanoff. — "  Ueber  die  Galvanischen  Erscheinungen  in  der  Haut  des 

Menschen,"  u.s.w.,  Pfiuger's  Archiv,  xlvi.,  p.  46,  1890. 
Leduc. — "Action  des  Courants  Continus  sur  I'Organisme  Vivant,"  A?iftales 

d'' Electrobiologie,  1901,  p.  261. 
Waller. — "On    Skin-currents.         Part    III, — The    Human    Skin,"   Proc. 

Roy.  Soc,  vol.  70,  p.  374,  1902, 


LECTURE   VIII 

The  Fallacy  of  the  Electrodes — Water  Transport  at  Anode  or  Kathode — 
Alteration  of  Resistance  at  Anode  or  Kathode. 

§  76.  Review. — This  lecture  is  to  be  partly  retrospective, 
partly  prospective.  We  shall  pass  under  a  rapid  review  the 
principal  steps  of  our  investigation,  inspecting  with  most  care 
what  may  appear  to  us  to  be  weak  points,  finding  perhaps  in 
those  very  weak  points,  points  of  attraction  to  further  investiga- 
tion. 

The  main  principle  and  "motif"  running  through  the  in- 
vestigation has  been  that  the  electrical  responses  to  electrical 
stimulation  are  a  token  and  measure  of  vitality  in  the  objects 
selected  for  examination — in  the  retina,  in  the  entire  eyeball,  in 
its  crystalline  lens,  in  the  skin  of  animals,  in  the  "  skin "  of 
plants,  in  all  the  living  tissues  of  plants,  in  living  tissues  of 
animals ;  and  in  my  last  lecture,  when  I  tried  to  show  you  how 
slowly  and  gradually  the  vitality  of  human  skin  is  lost,  I 
ventured  to  touch  upon  a  fallacy  that  becomes  specially 
apparent  when  one  undertakes  to  follow  the  sign  to  its  last 
discernible  trace.  It  was  lost  to  sight  among  accessory 
physical  reactions,  fortunately  small  as  compared  with  the 
physiological  reactions  of  full  vigour,  but  quite  unavoidable, 
since  they  are  inherent  to  the  apparatus  we  have  to  use,  I 
mean  the  electrodes.  And  although  I  call  your  special  atten- 
tion to  the  "  Fallacy  of  the  Electrodes "  at  this  last  stage,  I 
should  like  to  assure  you  that  it  has  been  carefully  excluded 
in  all  the  experiments  you  have  witnessed,  and  that  from  the 
very  outset  of  the  investigation  the  possible  simulation  of  a 
blaze-current  by  a  polarisation  at  the  electrodes  has  been  con- 
sidered and  excluded.    You  remember,  no  doubt,  that  we  hardly 

129  J 


130  THE  SIGNS  OF  LIFE  [lect. 

ever  omitted  to  control  the  result  observed  on  the  living  thing 
by  the  identical  test  applied  to  the  same  thing  killed. 

§  ']'].  Fallacies.  —  Fallacy  of  the  electrodes  arises  from 
polarisation ;  our  "  unpolarisable "  electrodes  are  not  abso- 
lutely unpolarisable,  and  may  accidentally  be  quite  sensibly 
polarisable.  Their  polarisation  currents,  anomalous  or  positive, 
as  well  as  normal  or  negative,  are  most  manifest  with  a  constant 
current,  much  less  so,  but  still  sensibly  so,  with  induced  currents. 
We  have  made  use  of  induced  currents  only,  and  shall  therefore 
restrict  our  attention  to  these. 

With  single  shocks  I  do  not  think  there  is  any  liability  to 
fallacy ;  an  unequivocal  or  homodrome  blaze-current  cannot  be 
simulated  by  anomalous  polarisation,  which  is  a  rare  and  feeble 
effect  manifested  by  a  defective  electrode,  and  quite  absent 
from  a  properly  prepared  electrode.  An  equivocal  or  anti- 
drome  blaze-current  might  at  first  sight  be  taken  as  being  due 
to  ordinary  polarisation,  since  it  is  of  the  same  direction  ;  but  the 
magnitude  of  the  response,  its  absence  from  the  electrodes 
themselves  when  joined,  and  from  the  tissue  itself  when  killed, 
will  leave  us  in  no  doubt  as  to  the  physiological  character  of  the 
reaction.  It  is  only  in  the  cases  where  single  shocks  having 
proved  to  be  ineffective,  we  have  recourse  to  the  further  test 
of  tetanisation  by  alternating  currents,  in  order  to  bring  out  a 
summated  effect  (p.  68),  that  there  is  any  real  possibility  of 
deception.  Distinguish  between  the  two  cases:  (i)  that  in 
which  the  alternating  currents  are  passed  through  the  galvano- 
meter and  test-object ;  (2)  that  in  which  they  are  passed  through 
the  test  object  only  while  the  galvanometer  is  short-circuited. 
The  first  of  these  two  dispositions  reproduces  an  arrangement 
that  was  first  adopted  by  V.  Fleischl  in  the  case  of  nerve,  and 
that  I  have  already  considered  at  some  length  in  that  connec- 
tion. The  opposed  make-and-break  currents  are  supposed  to 
neutralise  each  other  through  the  galvanometer,  and  such  deflec- 
tion as  occurs  is  attributed  to  an  electro-motive  action  of  the 
test-object.  This  deflection  occurs  in  the  direction  of  the  break 
current,  i.e.^  is  such  as  would  be  produced  by  a  physiological 
reaction  in  that  direction,  or  as  a  physical  reaction — the  sum 


VIII.]  FALLACY  OF  THE  ELECTRODES  131 

of  counter-currents  at  make  exceeding  the  sum  of  counter- 
currents  at  break.  A  closer  scrutiny  of  the  conditions  of  the 
reaction  shows  that  both  factors  are,  or  may  be,  effective,  i.e.,  a 
physiological  reaction  in  the  direction  of  break  can  occur  by 
reason  of  post-anodic  action-current,  and  a  physical  reaction  in 
that  same  direction  can  be  due  to  an  algebraic  sum  of  ordinary 
polarisation  currents.* 

It  is  not  quite  easy  to  clearly  demonstrate  the  physiological 
factor  even  in  a  favourable  case,  and  practically  impossible  to 
do  so  in  an  unfavourable  case ;  I  have  therefore  not  made 
systematic  use  of  this  first  disposition  of  test. 

The  second  disposition,  by  which  only  the  after-effect  of 
tetanisation  is  observed  on  the  galvanometer,  is,  in  my  experi- 
ence, less  liable  to  be  misleading  than  the  first.  But  the 
case  to  which  I  systematically  applied  it,  viz.,  the  human  skin, 
has  been  a  somewhat  favourable  one  to  follow  out,  since  by 

Skin  Living  Dead 

brecSik  ■< -« 

Response 

mca.ke 


Response 


reason  of  its  physiological  disposition  the  skin  gives  sign  of 
life  by  an  outgoing  response  to  all  directions  of  induction 
currents.  Tetanisation  by  such  alternating  currents  provokes, 
first,  a  summation  of  physiological  (outgoing)  effects ;  second, 
a   resultant   of   alternated  polarisation  effects  which  is  in    the 

*  Von  Fleischl's  deflection  is  discussed  at  some  length  in  Animal 
Electricity,  pp.  115-119,  1897.  The  superior  polarisation  by  make  there 
alluded  to  is  shown  in  a  paper  to  the  Physiological  Society  (12th  Nov. 
1898),  on  the  "Influence  of  Polarisation  on  the  Electrical  Resistance  of 
Nerve."  A  deflection  in  the  direction  of  break,  during  the^  passage  of  alter- 
nating induction  shocks,  might  also  be  due  to  an  irreciprocal  resistance, 
smaller  to  the  break  than  to  the  make  shock,  as  occurs  in  the  passage  of 
alternating  currents  through  a  vacuum  tube.  I  have  not  undertaken  the 
physical  analysis  of  these  possible  factors,  and  have  simply  abstained  from 
using  von  Fleischl's  deflection  as  a  sign  of  life. 


132  THE  SIGNS  OF  LIFE  [lect. 

direction  of  the  break  current.  Therefore,  if  to  both  pairs  of 
directions  of  tetanisation  the  after-effect  is  in  one  (positive  or 
outgoing)  direction,  we  have  proof  that  the  skin  is  alive ;  if  to 
both  pairs  of  directions  it  is  in  the  direction  of  the  break,  we 
have  proof  that  it  is  dead. 

I  found  it  at  first  not  a  Httle  confusing  that  a  deflection  in 
the  direction  of  the  break  current  —  which  in  V.  Fleischl's 
experiment  on  nerve  is  generally  considered  as  a  sign  of  life — • 
should  on  skin  (and  on  other  killed  tissues)  be  a  sign  of  death, 
But  evidently  the  deflection  in  question  is,  by  reason  of  the 
physical  factor  mentioned  above,  a  balance  of  ordinary  polari- 
sation in  the  direction  of  break.  Here  is  the  analysis  of  this 
pTiysical  resultant  for  the  two  pairs  of  tetanisation  directions  : — 

/.  Mdke     current,        — • >►  <s 

z.lcs  pob<a.ri-sa.t:ion       < >- 

£.Breca.k  currenC         < >■ 

4./CS  poLczrisACion      >  < 

/?esuLCc3.nC        < >- 


the  resultant  in  each  case  being  due  to  the  summated  effects, 
No.  2  being  greater  than  the  summated  effects  No.  4,*  You 
ask,  perhaps — if  you  have  followed  the  argument  so  far — why 
it  should  be  preferable  to  observe  an  after-effect  of  tetanisation 
rather  than  an  effect  during  tetanisation.  Ought  not  a  positive 
outgoing  eflect  to  manifest  itself  during  as  well  as  after  tetani- 
sation ?  So  it  does,  with  a  lively  skin,  that  will  respond  to 
strengths  of  tetanisation  that  can  be  passed  through  the 
galvanometer ;  such  a  skin  will,  however,  also  respond  to  the 
simpler  question  of  single  induction  shocks ;    a  skin  so  little 

*  This  result  maybe  observed  ;  with  strong  tetanisation  the  resultant  may 
be  in  the  direction  of  make,  the  after-effect  of  the  summated  effects  No.  4  being 
greater  than  that  of  the  summated  effects  No.  2.  Yet  even  in  this  case  the 
effect  during  tetanisation  is  in  the  direction  of  the  break.  I  am  not  certain 
whether  the  after-deflection  in  the  direction  of  the  make  is  physiological  or 
purely  physical.  I  place  no  reliance  whatever  upon  the  deflections  obtained 
dicring  strong  tetanisation.  They  can  happen  by  aUerations  of  the  gal- 
vanometer magnets  by  the  opposed  long  and  short  currents,  or  by  reason 
of  asymmetry  of  the  magnetic  field  in  the  absence  of  any  electrolyte  at  all 
in  circuit,  or  by  reason  of  irreciprocal  resistance. 


viri.]  QUINKE  CURRENTS  133 

alive  as  to  require  a  series  of  shocks  to  bring  about  summation 
of  effects,  must  be  tested  by  tetanisation  that  cannot  be  passed 
through  the  galvanometer,  which,  therefore,  must  be  short  cir- 
cuited during  the  process. 

There  is  one  more  shape  in  which  the  fallacy  of  the  elec- 
trodes may  appear,  which,  under  certain  conditions,  may  be 
very  deceptive  indeed.  The  state  of  the  electrodes,  especially 
if  they  have  been  long  put  up,  may  be  such  that  anomalous 
polarisation  of  one  electrode  may  be  present,  with  ordinary 
polarisation  of  the  other  electrode.  The  seat  of  such  polarisa- 
tion may  be  between  zinc  and  zinc  sulphate,  or  between  zinc 
sulphate  and  saline  clay.  The  deflection  may  be  in  one  and 
the  same  direction  for  both  pairs  of  directions  of  tetanisation, 
thus  simulating  the  formula  given  above  as  characterising  the 
living  state.  Electrodes  of  this  nature  must  not  be  used. 
Electrodes  prepared  with  ordinary  care  do  not  exhibit  the  fallacy. 

§  78.  A  future  prelifninary. — A  methodical  examination  by 
the  ABC  method,  of  the  polarisation  effects  produced  by  con- 
stant and  by  induced  currents  passed  through  various  electrodes 
and  electrolytes,  would  form  a  very  useful  preliminary  exercise 
introductory  to  the  study  of  physiological  polarisation.  You 
would  find  that  some  combinations  are  polarisable  at  both 
poles,  that  others  give  only  anodic  or  only  kathodic  polarisa- 
tion, and  prominent  among  these  purely  physical  effects  you 
would  find  that  by  reason  of  anomalous  polarisation  the  chief 
physiological  after-current — the  positive  post-anodic  action 
current — is  exactly  imitated,  which  things  should  not  lead  you 
to  imagine  that  the  physiological  effects  are  "  merely  physical," 
but  invite  you  rather  to  the  further  physical  analysis  of  physio- 
logical phenomena. 

§  79.  Quinke  currents. — Currents  of  liquid  through  a  porous 
partition,  e.g.^  a  membrane  through  which  osmose  is  taking 
place,  arouse  electrical  currents  in  the  direction  of  the  water 
movement.  Conversely,  an  electrical  current  passed  through  a 
porous  partition  between  two  electrolytes  causes  a  flow  of  water 
in  its  own  direction.     This  water  transport,  from  anode  towards 


134  THE  SIGNS  OF  LIFE  [lect. 

kathode — kataphoresis — is  a  chief  factor  in  the  electrical  osmose 
first  made  known  to  us  by  the  investigations  of  Ouinke.  ;=^ 

Our  attention  is  naturally  directed  to  the  question  of  such 
water  transport  through  porous  bodies  by  a  very  remarkable 
diminution  of  resistance  that  occurs — in  skin,  in  leaves,  etc. — as 
a  consequence  of  the  passage  of  induction  shocks.  This  diminu- 
tion of  resistance,  or  augmentation  of  conductivity,  is  far  more 
pronounced  in  living  than  in  dead  matter,  and  a  diminution  of 
resistance  in  consequence  of  molecular  dissociation  of  active 
stuff  must  therefore  be  thought  of 

I  think  it  probable  that  both  factors  contribute  to  the  result  ; 
their  experimental  distinction  and  separate  examination  appears 
very  desirable,  but  very  difficult. 

It  is  indeed  easy  enough  to  witness  what  must  be  an  effect 
of  kataphoric  water  movement  on  an  inert  object,  such  as  an 
eggshell ;  it  is  the  distinction  between  effects  of  kataphoresis 
and  a  dissociation  on  a  living  object  that  is  difficult.  The  best 
thing  that  can  be  hoped  for,  is  to  find  cases  where  one  factor  is 
predominant  and  the  other  insignificant.  In  a  muscle,  e.g.,  we 
may  expect  to  get  most  distinct  evidence  of  dissociation  ;  Loeb* 
has,  in  fact,  shown  that  the  osmotic  pressure  of  muscle  is  con- 
siderably augmented  by  tetanisation,  resting  muscle  being 
isotonic  with  a  0.6  per  cent.  NaCl  solution,  tetanised  muscle 
with  a  i.o  per  cent,  solution.  We  should  accordingly  expect  to 
find  an  increased  conductivity  in  active  muscle,  perhaps  also  in 
active  nerve — as  was  supposed  to  be  the  case  by  Griinhagen.  I 
have  not  yet  found  time  to  carry  out  such  experiments  ;  perhaps 
someone  among  my  present  hearers  will  take  them  in  hand. 

The  following  experiment  has  been  put  up  to  show  this 
purely  physical  effect  of  kataphoresis ;  it  will  at  the  same  time 
serve  to  illustrate  another  of  the  fallacies  that  might  deceive  an 
inexperienced  observer. 

An  eggshell  (with  its  membrane)  has  been  set  up  between 
the  exploring  electrodes  to  be  examined  in  the  usual  way. 
From  a  compensator  I  pass  yi^  volt  through  the  shell  and 
galvanometer ;   the   deflection    is   ^2   degree   of  scale,      I    pass 

*  Loeb,  "  Physiologische  Untersuchungen  iiber  lonenwirkungen  (I  Ver- 
suche  am  Muskel),"  Pfliiger's  Archiv,  Ixix.,  p.  i,  1898,  and  Ixxi.,  p.  457. 


viii.]  EVAPORATION  CURRENTS  135 

strong  alternating  induction  currents  through  the  eggshell 
(plugging  out  the  galvanometer  meanwhile),  and  then  again 
pass  yijj-  volt  through  the  eggshell  and  galvanometer.  The 
deflection  is  now  20  degrees  of  scale,  z>.,  the  conductivity,  by 
reason  of  water  transport  from  electrodes  to  shell,  has  been 
increased  more  than  fortyfold. 

A  propulsion  of  water,  through  capillary  pores,  by  an 
electrical  current,  might  conceivably  outlast  its  original  cause. 
And  since  a  capillary  current  can  give  rise  to  an  electrical 
current  in  its  own  direction,  it  is  conceivable  that  a  homodrome 
after-current  might  be  thus  brought  about.  I  have  at  various 
times  made  a  good  many  trials  of  this  point,  with  porous  septa 
Df  various  kinds  between  saline  solutions  of  various  strengths, 
without  ever  observing  anything  at  all  comparable  with  an 
unequivocal  blaze-current  of  a  living  object.  Here  is  an 
ordinary  dialysing  tube  containing  a  strong  solution  of  zinc 
sulphate,  and  surrounded  by  a  weaker  solution ;  two  amalga- 
mated zinc  rods  dipping  in  the  fluid  on  each  side  of  the  septum, 
serve  as  electrodes ;  the  dialysing  cell,  compensator,  induction 
coil  and  galvanometer  are  connected  to  the  keyboard  in  the 
usual  way.  Notice,  in  the  first  place,  the  normal  current — from 
less  concentrated  to  more  concentrated  solution  in  the  dialysing 
cell,  i.e.^  "  with  "  the  water  current,  and  from  more  to  less  through 
the  galvanometer.  And  now,  with  this  concentration  current 
compensated,  I  send  a  strong  break  shock  through  the  dialyser 
first  from  B  to  A,  when  you  see  a  polarisation  deflection  from  A 
to  B  ;  then  from  A  to  B,  when  you  see  a  polarisation  deflection 
from  B  to  A.  And  I  do  not  stop  to  inquire  whether  these 
polarisation  counter-currents  are  at  the  electrodes  or  at  the 
interface  of  the  two  solutions  ;  for  they  are  antidrome  effects, 
and  we  are  now  looking  for  homodrome  effects. 

So  we  find  that  although  no  doubt  water  transport  through 
pores  occurs  in  living  as  well  as  in  dead  matter,  and  contributes 
no  doubt  to  augmented  conductivity  caused  by  electrical  currents, 
it  cannot  be  made  responsible  for  the  currents  now  familiar  to 
us  as  blaze-currents  ;  the  sme  qua  non  of  these  currents,  what- 
ever their  chemico-physical  mechanism  may  ultimately  prove  to 
be,  is  the  living  state. 


136 


THE  SIGNS  OF   LIFE 


[lect. 


And  yet,  while  we  find  reason  to  reject  an  appeal  to  water 
currents  (or  "  concentration  currents "),  as  being  the  original 
source  of  electrical  effects  that  arise  or  are  provoked  in  living 
matter,  we  should  be  careful  to  remember  that  water  currents 
must  actually  play  an  important,  if  secondary  part,  in  the  com- 
plicated molecular  play  of  physiological  action.  Local  action 
implies  local  disintegration,  raised  osmotic  pressure,  attraction 
of  water,  and  electrical  current.  The  water  current  is  towards 
the  active  spot ;  the  electrical  current  is  from  that  spot ;  we 
must  imagine  it  as  a  kationic  current. 

§  80.  Evaporation  current. — This  first  experiment  should 
serve  as  reminder  to  you  that  gradual  shiftings  of  the  galvano- 

(         ) 


Fig.  54. — To  illustrate  evaporation  currents. 

meter  spot  may,  among  other  causes,  be  due  to  evaporation  of 
water,  and  to  capillary  currents  thereby  produced.  The  circuit 
contains  nothing  but  the  galvanometer,  and  a  pair  of  unpolaris- 


vin.]  CONCENTRATION  CURRENTS  137 

able  electrodes,  the  clay  of  which  has  been  so  shaped  as  to  give 
dissimilar  surfaces  of  evaporation.  The  clay  is  moist,  the  air  of 
the  room  is  dry,  B  is  giving  off  water  more  quickly  than  A, 
and  is  sucking  water  from  A,  so  the  electrode  current  is  to  your 
left,  as  figured.  I  now  bring  down  over  the  electrodes  a  bell- 
jar  with  a  bit  of  wet  blotting  paper  sticking  inside  it,  i.e.,  con- 
taining wet  air.  The  galvanometer  spot  is  sharply  deflected  to 
your  right  (by  the  checked  or  reversed  water  current).  On 
removal  of  the  bell-jar  the  spot  is  sharply  deflected  to  the 
left  (evaporation  current  to  room  air),  and  finally,  when  the 
evaporation  and  deflection  have  become  steady,  I  cover  the 
electrodes  with  a  dry  heated  bell-jar,  which  at  once,  by  accelerat- 
ing the  evaporation,  causes  a  sharp  deflection  to  the  left.  And 
for  the  present  I  am  not  concerned  to  know  whether  or  no  the 
concentration  of  saline  solution  plays  a  part  in  these  evaporation 
effects ;  all  I  want  to  do  is  to  show  you  that  trifling  altera- 
tions of  evaporation  can  give  quite  considerable  electrical 
effects. 

§  8 1.  Concentration  ciirre7it. — The  next  experiment  is  intended 
to  remind  you  of  the  usual  direction  of  a  concentration  current 
— a  point  which  in  most  text-books  and  monographs  appears  to 
be  considered  as  too  self-evident  to  be  worth  specifying.  Two 
amalgamated  zinc  rods  dip  into  a  25  per  cent,  solution  of  zinc 
sulphate,  and  are  connected  with  the  galvanometer. 

A  drop  of  distilled  water  allowed  to  run  down  B  into  the 
solution  gives  deflection  to  your  right  (current  from  B  to  A). 
A  drop  of  saturated  zinc  sulphate  to  B  gives  deflection  to  your 
left  (current  from  A  to  B). 

And  of  course  dilution  at  A  gives  deflection  to  the  left,  con- 
centration at  A  gives  deflection  to  the  right.  In  terms  of  the 
ionic  movements,  this  happens  by  reason  of  greater  velocity 
of  the  anion  (which  travels  from  the  more  concentrated  to  the 
less  concentrated  solution,  giving  therefore  current  in  the  reverse 
direction).  With  acids,  e.g.,  HCl,  and  complex  organic  salts, 
e.g.,  CII3COOK,  in  which  the  kation  travels  faster  than  the 
anion,  the  current  is  from  more  to  less  concentrated  solution. 
But  with  all  our  ordinary  neutral  salts,  and  with  alkalies,  the 


138  THE  SIGNS  OF  LIFE  [lect. 

current   is   from    dilute    to   concentrated,   i.e.,   with   the   water 
current. 

The  direction  of  electrical  current  between  two  unequally 
concentrated  solutions  of  any  electrolyte  depends  upon  the 
relative  velocities  of  the  two  ions,  both  of  which  are  of  course 
travelling  from  concentrated  to  dilute  solution.  If  the  anion  is 
of  higher  velocity,  as  is  the  case  with  alkalies  and  most  salts,  the 
current  is  from  dilute  to  concentrated  ;  if  the  kation  is  of  higher 
velocity,  as  is  the  case  with  acids  and  some  salts,  the  current  is 
from  concentrated  to  dilute.  (See  Fig.  55.)  You  may  be  dis- 
posed to  admit  provisionally,  as  I  do,  that  the  latter  condition 
obtains  in  the  case  of  the  complex  organic  compounds  that  take 
part  in  the  dance  of  life ;  current  of  action  proceeding  from  the 
spot  of  greatest  "  livingness,"  where  solution  pressure  is  in- 
creased —  and  dissociation  —  and  ionic  concentration  —  and 
osmotic  pressure. 

Some  Relative  Ionic  Velocities. 

Kation  +  Anion  - 

NaCl               Sodium         37  Chloride     63 

HCl                 Hydrogen     80  Chloride     20 

NaOH             Sodium         20  Hydrate     80 

CH3COOK     Potassium     68  Acetate      32 

Some  Absolute  Ionic  Velocities. 
(At  P.D.  of  I  volt  per  i  cm.,  and  Temp,  of  18°  C.) 

In  cm.  per  sec.  In  mm.  per  hour. 

Hydrogen         H  +                              0.00320  115 

Hydroxy!          OH  -                           0.00182  65 

Sodium             Na  +                            0.00045  16 

Chlorine            CI  -                              0.00069  25 

Potassium         K  +                               0.00066  24 

Acetyl               CH3COO  -                 0.00036  13 

Engelmann  in  the  course  of  his  investigation  of  skin 
currents,  and  Biedermann  in  his  examination  of  mucous 
currents,  paid  particular  attention  to  the  effects  of  water,  and 
of  saline  solutions  on  the  normal  current.  Neither  of  these 
authors  explicitly  distinguishes  the  physical  imbibition  current, 
which  must  evidently  have  been  a  considerable,  if  not  the  chief 


VIII.] 


CONCENTRATION  CURRENTS 


139 


or  sole  efficient  cause  of  the  effects.     If  you  refer  to  the  detailed 
accounts  given  by  Engelmann,*  and  by  Biedermann.f  you  will 


Concert  I: rabei. 
A 


->v36 


->  6^ 


\^,  \Currenb 
(  //  + 

I       a  - 

\.,\Currenb  — ■ ■"■■i" »> 


-^320 


-^69 


->66 


-^/32 


J^69 


-^ee 


-^36 


I  OH- 

\.,\Currenb 

\  ^^  " 

\,,l  Current 

{  ^  1 

i     CH^.CO.O. 

\^,'.  Current        » 

Fig.  55- — To  illustrate  concentration  currents.  The  thin  arrows  indicate  direction 
of  ions  from  concentrated  to  dilute  side  of  an  electrolyte.  The  thick  arrow  in  each 
case  indicates  the  resultant  current — from  dilute  to  concentrated  where  the  anionic 
is  higher  than  the  kationic  velocity  ;  from  concentrated  to  dilute  where  the  kationic 
is  higher  than  the  anionic  velocity.  (The  relative  ionic  velocities  are  indicated  by 
the  numbers  at  the  arrow-heads.) 

N.B. — With  the  kation  travelling  from  left  to  right,  there  is  current  from 
left  to  right,  and  vice  versa. 

With  the  anion  travelling  from  left  to  right,  there  is  current  from  right  to 
left,  and  vice  versa. 


find  that  a  large  ingoing  effect  was  generally  produced  by  water 
or  weak  saline,  a  large  outgoing  effect  by  strong  saline.     The 

*  Engelmann,  P.  A.,  vi.,  p.  no. 

t  Biedermann,  Elektrophysiologie,  p.  401. 


140  THE  SIGNS  OF  LIFE  [lect. 

former  is  such  as  would  be  produced  by  an  ingoing  current  of 
water  through  the  skin,  the  latter  by  an  outgoing  current  of 
water.  The  effects  appear  to  be  similar  in  character  to  those 
more  recently  pointed  out  by  MacDonald,  as  regards  the 
injury  current  of  nerve — which  he  considers  as  being  essentially 
a  concentration  current — viz.,  augmentation  by  water  or  by 
dilute  salt  solution,  diminution  or  abolition  by  strong  salt 
solution. 

§  82.  A  limitation. — While  it  is  perfectly  true  that  blaze  is 
a  sign  of  life,  it  is  equally  true  that  many  assuredly  living  things 
do  not  blaze.  But  at  this  stage,  without  a  fuller  and  more 
exhaustive  examination  of  all  sorts  and  conditions  of  living 
matter,  it  would  be  hazardous  to  propound  any  absolute  and 
unrestricted  negation.  In  the  more  familiar  case  of  the  evolution 
of  CO2,  we  know  that  the  phenomenon  is  a  sign  of  life  ;  but  we 
also  know  that  many  assuredly  living  things  do  not  demonstrably 
discharge  CO.2,  and  that  the  same  living  things  may  comport 
themselves  very  differently  under  different  conditions.  The  low 
resistance  of  organs  like  the  liver  and  kidney,  the  absence  of  a 
definite  membrane  between  our  electrodes  enabling  living  cells 
to  exercise  the  osmotic  pressure  that  underlies  ionic  transfer, 
are  conditions  obviously  unfavourable  to  the  delivery  of  blaze- 
currents  into  an  external  circuit. 

Many  assuredly  living  things  have  not,  to  such  examination 
as  we  have  as  yet  made,  manifested  the  clear  and  typical  effects 
familiar  to  us  in  the  case  of  the  eye,  and  the  skin  and  vegetable 
tissues.  Muscle  and  nerves  give  comparatively  small  effects, 
and  I  have  even  failed  to  obtain  any  trace  of  respopse — under 
similar  conditions  of  experiment — from  the  recently  excised 
organ  of  torpedo  which  a  few  moments  before,  in  the  animal 
itself,  gave  me  the  well-known  thrill  characteristic  of  the  dis- 
charge. I  have  witnessed  well-marked  effects  in  frog's  spawn 
at  one  time,  and  have  failed  to  obtain  any  effect  at  all  in  other 
spawn  at  a  different  stage  of  development.  I  do  not  conclude 
from  this  that  blaze  is  not  a  sign  of  life  ;  indeed,  I  should  be 
reluctant,  without  further  and  closer  examination — by  the  ABC 
method,  and  with  shortest  possible  transfer  time — to  state  abso- 


viii.]  A  LIMITATION  141 

lutely  that  any  given  object  exhibits  no  blaze  at  all.  The  ' 
internal  organs  certainly  do  not  blaze  like  the  skin,  or  even  like 
nerve,  the  failure  is  in  itself  of  interest,  and  the  cause  of  differ- 
ence matter  for  investigation,  and  we  shall  have  to  learn  what  is 
the  determinant  factor  between  a  living  tissue  that  manifests 
blaze,  and  another  living  tissue  that  does  not.  Durig  thinks 
that  the  effect  is  peculiar  to  epithelial  tissues,  and  it  is  certainly 
the  case  that  epithelial  tissues  do  give  it  better  than  other 
tissues — witness  the  case  of  the  crystalline  lens.  But  I  do 
not  think  it  is  confined  to  epithelia,  for  it  occurs  in  muscle, 
and  in  vegetable  tissues  which  can  scarcely  be  classed  as 
epithelial. 

I  am  unwilling  to  express  any  opinion  at  all.  I  have 
witnessed  it  in  muscle ;  witnessed  it  in  some  frog's  spawn, 
and  failed  to  witness  it  in  other  frog's  spawn.  Does  it  depend 
upon  some  regular  orientation  of  cells  ?  Is  their  regular 
arrangement  on  a  basement  membrane  a  favouring  condition 
of  things?  What  part  do  membranes  play  in  the  effect? 
These  are  questions  all  of  which  I  must  leave  unanswered 
now. 

In  two  successive  years  I  took  occasion  to  examine  seaweeds, 
with  the  object  of  comparing  their  reactions  with  those  of  land 
plants.  To  my  considerable  surprise,  they  gave  little  or  no 
reaction,  and  I  left  the  seaside  on  the  first  occasion  without 
having  been  able  to  satisfy  myself  of  the  physiological  nature  of 
such  small  reactions  as  were  occasionally  witnessed.  The  "  weeds  " 
— obtained  in  the  Channel  Islands  in  an  obviously  living  state 
during  the  month  of  August — always  gave  small  antidrome 
after-currents  at  both  poles  to  single  shocks  as  if  by  ordinary 
polarisation.  But  the  effects  were  abolished  by  boiling.  This 
was  a  puzzle,  and  I  cannot  yet  explain  it.  The  elements  of 
the  problem  are :  deflections  antidrome  throughout,  therefore 
apparently  ordinary  polarisation ;  but  abolished  by  boiling, 
therefore  apparently  of  a  physiological  character. 

Pieces  of  apple  gave  a  similar  puzzle,  viz.,  antidrome  effects 
abolished  by  boiling,  and  it  is  possible  in  such  cases  that  we 
have  to  do  with  a  mere  physical  effect  of  altered  structure  or 
altered  composition,  possessing  no  physiological  significance. 


142  THE  SIGNS  OF   LIFE  [lect. 

On  the  second  occasion  after  several  trials  with  negative 
results,  I  excited  the  cupidity  of  my  children  by  the  offer  of 
a  reward  for  a  blazing  seaweed,  and  was  myself  rewarded  by 
their  discovery  of  a  long,  narrow  seaweed,  called  "  boot  laces  " 
by  the  fishermen — chorda  filum  by  its  museum  name — that 
gave  typical  homodrome  effects  of  more  than  0.02  volt  to  both 
directions  of  excitation,  and  therefore  saved  me  from  saying 
that  sea-plants  unlike  land-plants  do  not  blaze.  The  difference 
between  the  two  kinds  of  vegetable  is  indeed  very  marked,  but 
it  is  one  of  degree  rather  than  of  kind,  and  one  of  the  chief 
conditions  of  the  difference  is  that  the  former  are  bad  and  the 
latter  good  conductors.  Evidently,  if  the  resistance  of  the 
inactive  stuff  between  our  electrodes  is  so  low  as  to  afford 
great  internal  shunting,  an  electromotive  change,  unless  very 
large,  will  not  give  much  current  to  a  high  resistance  galvano- 
meter. 

The  common  animals  of  the  sea  shore — limpets,  anemones, 
jelly-fish,  etc. — afforded  little  or  no  response  to  the  usual  test  of 
single  and  of  tetanising  induction  shocks.  The  eyes  and  the 
muscles  of  crabs  and  lobsters,  the  eyes  and  the  skin  of  fishes 
(whiting,  sand  eel),  gave  very  well-marked  effects. 

But  we  should  not  hastily  conclude  that  the  absence  or 
smallness  of  blaze-currents  depends  on  conductivity  alone. 
Absence  of  blaze  depends,  also,  I  think,  upon  the  relatively 
small  amount  of  active  living  electromotive  stuff  in  the  mass 
of  indifferent  stuff  that  is  its  habitation.  Low-class  living 
matter,  pervaded  and  diluted  by  the  medium  in  which  it 
lives,  cannot  be  expected  to  exhibit  any  very  intense  sign 
of  life ;  we  do  not  expect  it  to  blaze  much.  The  mass  of  a 
jelly-fish  or  of  a  seaweed  is  in  chief  part  sea-water ;  its  living 
stuff  has  not  the  power  to  emancipate  itself  from  the  external 
medium,  nor  to  create  an  internal  medium,  different  and  distinct 
from  the  general  environment.  It  is  practically  isotonic  with 
sea-water ;  its  freezing  point,  and  that  of  sea-water,  are  both 
about  —  2°.  Like  sea-water,  it  contains  over  3  per  cent,  of  salts, 
and  its  conductivity  is  at  least  fifty-fold  that  of  land-plants. 
This  no  doubt  is  an  unfavourable  condition  to  the  production 
as  well  as  to  the  manifestation  of  a  local  alteration  of  potential. 


VIII. j         INJURY  CURRENT  AND  BLAZE-CURRENT  143 

But  we  may  hardly  proceed  further  on  these  hues  of 
argument  without  further  information  concerning  the  exact 
freezing  points  and  the  relative  conductivities  of  various  animal 
and  vegetable  tissues,  and  to  obtain  such  information  means 
engaging  in  a  new  investigation,  for  which  new  methods  have  to 
be  elaborated. 

§  83.  A  question. — It  has  probably  occurred  to  some  of  us  to 
ask  what  relation,  if  any,  exists  between  the  normal  current  and 
a  blaze-current.  Is  not  the  normal  current  itself  a  sign  of  life, 
and  in  certain  cases  of  obviously  identical  nature  with  a  blaze  ? 

To  some  extent  these  questions  have  been  incidentally 
answered  in  previous  lectures,  but  not  formally  and  explicitly. 

Indeed  it  is  difficult  to  frame  a  formal  and  explicit  answer, 
and  I  should  prefer  to  avoid  giving  such  an  answer  otherwise 
than  with  much  reservation.  For  the  facts  of  the  case  are  by 
no  means  as  clear  as  they  seem  to  be  at  first  sight.  As  regards 
the  first  question,  we  can  make,  with  about  equal  probability, 
the  two  apparently  contradictory  statements  that  in  some  cases 
there  is  an  evident  relation  between  normal  and  blaze-currents, 
in  other  cases  there  is  evidently  no  relation  at  all  between  the 
two  currents.  And  on  reflection  it  will  appear  that  our  first 
question  should  logically  be  preceded  by  our  second  as  to 
whether  normal  current  is  or  is  not  a  sign  of  life,  which  amounts 
to  asking  what  view  we  take  of  the  nature  of  normal  currents. 

Now,  I  think  you  may  take  as  granted  that  normal  current 
is  always  injury  current  or  excitation  current ;  but  I  do  not 
think  you  may  take  as  granted  that  injury  current  is  always 
excitation  current. 

The  question  of  the  nature  of  injury  current  has  largely 
turned  of  late  years  upon  the  demarcation  current  of  medul- 
lated  nerve  ;  in  opposition  to  the  view  of  Gotch,  who  assumes 
that  this  current  is  wholly  an  excitation  current,  MacDonald 
urges  that  it  is  a  concentration  current  dependent  upon  the 
electrolytes  of  nerve.  He  regards  nerve  as  a  concentration  cell 
in  which  the  sheath  is  the  dilute  solution  (=  0.9  per  cent.  KCl), 
the  axis-cylinder  the  concentrated  solution  (=10  per  cent.  KCl), 
and  the  current  determined  by  the  physico-physiological  state 


144  THE  SIGNS  OF  LIFE  [lect. 

of  a  membrane  between  sheath  and  axis.  It  would  lead  us  too 
far  to  discuss  this  theory  in  all  its  details.  My  own  opinion  of 
the  matter  is  that  MacDonald  has  sufficiently  proved  the  reality 
of  the  concentration  currents  of  nerve  by  the  annulling  effects  of 
strong  salt  solutions  and  by  the  recuperative  effects  of  weak 
salt  solutions,  but  that  he  has  not  disproved  the  irritative  factor. 
I  think  both  factors  are  concerned  in  the  current,  and  if  called 
upon  to  put  a  figure  upon  their  value,  should  guess  that  in  a 
fresh  demarcation  current  of  say  0.05  volt  something  like  0.04 
is  by  concentration,  and  0.0 1,  or  less,  by  irritation. 

To  return  to  the  first  question,  stated  at  the  outset  of  this 
paragraph,  I  should  tentatively  answer  that,  in  so  far  as  an 
"  injury  current "  is  irritation  current,  blaze-current  bears  relation 
to  it,  but  that  in  the  absence  of  irritation  current,  or  in  so  far 
as  "  injury  current "  is  of  mere  physical  origin,  blaze-current  is 
quite  an  independent  phenomenon. 

I  think  that,  on  this  view,  we  may  now  reconcile  with  each 
other  these  several  facts,  of  which  the  first  three  are  affirmative 
as  regards  a  relation  between  blaze-current  and  injury  current, 
the  last  negative. 

1st.  That  a  blaze-current  is  in  general  antidrome  to  an 
injury  current. 

2nd.  That  it  is  always  antidrome  to  a  previous  (maximal) 
blaze-current. 

3rd.  That  a  (polarising)  constant  current  favours  homodrome 
and  disfavours  antidrome  blaze-current 

4th.  That  in  some  cases  blaze-current  may  be  homodrome 
with  injury  current. 

5th.  That  in  many  cases — eyeball,  skin,  and  electrical  organ — 
there  is  no  discernible  relation  between  the  direction  and  mag- 
nitude of  normal  current  and  of  blaze-current. 

The  fact  that  a  blaze-current,  antidrome  to  an  injury  current, 
is  aroused  by  both  directions  of  excitation,  proves  of  itself,  what 
is  more  clearly  proved  by  the  ABC  method,  viz.,  that  the 
response  may  be  post-kathodic  as  well  as  post-anodic,  or,  in 
Biedermann's  phrase,  negative-kathodic  as  well  as  positive- 
anodic.  In  either  case  it  is  the  analogue  of  the  "  negative 
variation  "  of  a  demarcation  current  of  muscle  or  of  nerve,  where 


VIII.]  INJURY  CURRENT  AND  BLAZE-CURRENT  Ug 

it  is  known  to  us  as  a  transmitted  excitatory  effect,  whereas 
the  "  blaze  "  is  a  direct  excitatory  effect. 

The  fact  that  a  blaze-current  homodrome  with  its  exciting 
current,  is  obtained  between  two  uninjured  and  iso-electric  points, 
signifies  that  in  general  the  post-anodic  homodrome  is  greater 
than  the  post-kathodic  antidrome  current.  There  is  an  ex- 
citatory state  at  both  poles,  greater  at  anode  than  at  kathode, 
and  if  the  excitation  be  reversed,  there  is  as  before  a  homodrome 
effect,  but  reversed  with  the  reversal  of  excitation.  If,  before 
applying  the  second  stimulus,  we  shift  one  of  the  electrodes 
that  have  served  for  the  first  stimulus  and  blaze,  to  a  fresh  spot 
(or,  better,  if  by  the  ABC  plan  we  transfer  the  A  or  B  con- 
nections to  a  third  indifferent  point  C),  we  shall  find  (on  muscle, 
on  vegetables)  that  both  A  and  B — i.e.,  post-kathodic  and  post- 
anodic  points — are  zincative  (electro-positive)  to  C.  And  if,  now, 
having  compensated,  we  stimulate  in  either  direction  through 
these  points  A  C  or  B  C,  i.e..,  through  one  active  point  A  or  Bj 
and  one  passive  point  C,  we  shall  arouse  blaze  in  the  tissue  from 
C  to  A  or  B.  The  first  excitation  has  given  blaze  of  A  and  B, 
which  are  zincative  (electro-positive)  to  C.  The  second  excita- 
tion has  given  a  second  blaze  of  either  A  or  B,  which  is  opposed 
and  greatly  exceeded  by  the  first  blaze  of  the  previously  un- 
touched C.  We  may  regard  the  first  current  from  A  or  B  to  C 
as  an  injury  current,  and  the  second  current  from  C  to  A  or  B 
as  its  negative  variation. 

So  that  in  sum  total  we  assimilate,  as  belonging  to  one  class, 
what  has  been  variously  designated  blaze-current,  injury  current 
(in  so  far  as  it  is  an  irritation  current),  and  action  current.  The 
fact  that  a  blaze-current  is  augmented  where  it  occurs  in  the 
same  direction  as  a  polarising  current,  is  essentially  similar  with 
the  phenomenon  known  to  you  in  nerve-physiology  as  the 
polarisation  increment.  In  the  latter  case,  an  active  state  sweep- 
ing wave-like  along  a  nerve  undergoes  a  sudden  increment  on 
reaching  an  anodic  region,  and  the  polarising  current  is  in- 
creased ;  the  anodic  region,  in  which  action  is  lowered,  is 
capable  of  great  increase  of  action  when  it  is  aroused  by  the 
transmitted  excitation.  It  is  more  "  zincable."  In  our  case, 
also,  the  anodic  region  of  a  polarising  current  is  more  "  zincable," 

K 


146  THE  SIGNS  OF  LIFfi  '  [lect. 

i.e.,  more  capable  of  that  electro-positive  change  which  is  the 
essential  factor  of  a  blaze-current,  and  is  aroused  to  action  by 
the  direct  stimulus  of  an  induction  shock  whatever  its  direction. 

§  84.  Solution-pressure. — I  will  bring  these  lectures  to  a 
conclusion  with  certain  theoretical  views  to  which  slight  allusion 
was  made  in  the  first  lecture  (p.  16). 

I  there  attempted  to  account  in  some  measure  for  the  use  of 
the  term  "zincative,"  and  promised,  when  an  opportunity  should 
present  itself,  to  formulate  on  similar  lines  a  view  of  the 
mechanism  of  excitatory  phenomena  in  general. 

You  are  familiar  with  the  idea  that  active  tissue  gives  off 
electro-positive  ions  to  its  lymph  bath,  that  in  the  tissue  itself 
there  is  current  of  action  from  active  to  resting  spot,  that  active 
tissue  is  zincative.  You  also  know  that  in  the  electrical  excita- 
tion of  nerve  and  of  muscle,  the  effective  pole  is  the  kathode, 
when  current  is  made,  the  anode  when  current  is  broken.  And 
you  know  that  while  a  constant  current  is  passing  there  is 
augmented  excitability  by  the  kathode,  diminished  excitability 
by  the  anode. 

I  take  the  case  of  medullated  nerve,  since  the  results  are 
typical.  Moreover,  its  coarse  structure  of  central  core  as  the 
essential  part  and  surrounding  sheath  as  the  accessory  part, 
which  is  a  familiar  image  in  everyone's  mind,  will  help  us  to 
form  a  clear  picture  of  what  can  be  imagined  as  the  actual 
movements  of  ions  between  any  core  of  living  stuff  and  any 
surrounding  medium.  (A  word  of  warning,  however — this  is  only 
a  coarse  picture,  there  is  no  doubt  a  peculiar  commerce  of  ions 
between  axis-cylinder  and  medullary  sheath  of  a  nerve-fibre, 
but  there  is  probably  a  further  and  more  refined  commerce 
of  ions  between  fibrils  and  fluid  within  the  axis-cylinder 
itself) 

Consider  then  a  core  of  living  stuff,  bring  it  in  contact  with 
an  electrode,  and  let  the  latter  be  suddenly  made  kathodic  by 
closure  of  a  contact  key  in  the  circuit.  The  core  of  living  stuff 
has  been  aroused  to  action.  What  have  been  the  movements  of 
ions  when  the  electrode  was  made  kathodic  ? 

Clearly,  there  must  have  been  movement  of  kations  towards 


vni.]  SOLUTION-PRESSURE  147 

the  kathode,  of  anions  from  the  kathode — viz.,  attraction  of  the 
former,  repulsion  of  the  latter,  as  regards  the  surface  of  separa- 
tion between  core  and  bath. 

The  attraction  of  the  kation  to  the  surface  of  the  core  is  in 
this  view  of  the  matter  to  be  regarded  as  the  essential  factor  of 
excitation  (and  of  increased  excitability),  inasmuch  as  such 
attraction  is  equivalent  to  an  increased  "  solution-pressure "  of 
kations.  The  living  core,  under  the  influence  of  the  kathode,  is 
rendered  more  active  and  discharges  into  the  surrounding 
solution  a  greater  number  of  electro-positive  ions  since  the 
pressure-difference  of  such  ions  in  the  core  and  in  the  solution  is 
increased.  As  mentioned  in  a  previous  lecture,  this  is  the  state 
of  things  that  I  conceive  to  exist  when  I  make  use  of  the 
expression  that  active  (or  excited)  living  matter  is  "  zincative  " 
to  resting  living  matter.  I  imagine  "  current  of  action "  as 
being  conditioned  by  the  discharge  from  active  stuff  of  free 
kations,  and  I  choose  zinc  by  name  as  the  representative  kation. 

But,  you  say  perhaps,  why  have  you  specified  the  kation 
rather  than  the  anion  as  the  effective  agent  in  the  produc- 
tion of  an  action  current  ?  Is  not  current  from  an  excited  to 
an  unexcited  spot  accounted  for  by  a  transport  of  negative 
electricity  by  anions  towards  an  excited  spot,  as  well  as  by 
a  transport  of  positive  electricity  by  kations  away  from  an 
excited  spot? 

Or  again,  you  definitely  object  that  it  is  wrong  to  think 
of  kations  as  travelling  against  current,  or  anions  with  current. 
To  the  second  of  these  possible  objections  in  your  mind,  I 
answer  at  once  that  we  are  not  considering  simple  passage  of 
the  exciting  current  through  the  electrolyte,  but  the  excited 
current  arising  at  the  exciting  pole  of  the  former — viz.,  at  the 
kathode.  And,  if  you  are  in  any  doubt  about  this  kathodic 
action  current  produced  during  the  passage  of  the  exciting 
current,  perhaps  you  had  better  consider  on  similar  lines  the 
post-anodic  action  current  that  is  witnessed  after  an  exciting 
current  has  been  stopped.  In  this  case  we  clearly  have  to  do 
with  a  sudden  release  of  kationic  pressure,  as  the  repellant 
influence  of  the  anode  terminates. 

To  the  first  point — I  have  to  offer  you  at  least  two  consider- 


148  THE  SIGNS  OF  LIFE  [lect. 

ations  in  support  of  my  choice  of  the  kation  rather  than   the 
anion  as  the  principal  carrier  in  the  case  of  an  action  current. 

We  have  regarded  the  tension  and  solution-pressure  of 
metallic,  basic,  positive  sign  as  increased  at  the  surface  of  the 
living  core  under  the  influence  of  the  negative  pole. 

Under  this  same  influence  we  should  also  have  a  decreased 
tension  and  solution  pressure  of  non-metallic,  acidic,  negative 
sign. 

This  second  mode  of  transport  seems  to  me  to  imply  neces- 
sarily the  diminution  of  a  pre-existing  state  of  difference ; 
whereas  the  kationic  nature  of  an  action  current  does  not 
necessarily  imply  any  pre-existing  state  of  difference.  No 
doubt,  as  a  rule,  all  living  matter  is  at  least  sub-active  at  low 
pressure  within  its  internal  medium,  the  lymph.  But  that  is 
"pre-existing  difference"  of  very  different  order  to  a  pre- 
existing difference  great  enough  to  permit  of  the  great  diminu- 
tions of  difference  that  should  be  caused  by  great  augmentation 
of  activity  and  of  pressure. 

On  these  general  grounds,  therefore,  without  wholly  dis- 
regarding the  possibilities  of  anionic  transport,  I  have  chosen 
to  consider  action  currents  as  effected  by  kationic  transport  from 
the  seat  of  action  rather  than  by  anionic  transport  towards  the 
seat  of  action.  And  I  say  again  on  these  grounds,  as  well  as 
for  reasons  given  in  a  previous  lecture,  that  active  living  matter 
is  zincative. 

One  further  reason  for  this  preference  of  the  kationic  to  the 
anionic  view  of  action  currents  (vegetable  as  well  as  animal,  I 
may  remark)  may  be  briefly  mentioned  now,  in  anticipation  of 
evidence  that  I  hope  to  more  fully  place  before  you  at  some 
future  occasion. 

You  know  that,  according  to  modern  theory,  the  molecules  of 
a  neutral  salt,  such  as,  e.g.,  NaCl  in  aqueous  solution,  exist  not 
solely  as  non-electrical  molecules  of  NaCl,  but  also  (and  in  dilute 
solutions  chiefly)  as  charged  ions  Na-l-  and  CI-  .  In,  e.g.,  what 
we  ordinarily  call  "  normal  saline  "  in  the  laboratory,  made  up 
to  contain  ^V  grammolecule  per  litre  of  water,  z>.,  5.84  grammes 
per  litre,  y'^j-of  the  amount  of  salt  is  present  in  the  dissociated  or 
ionised   state   as    Na-j-    and    CI  - ,  and  the  only  uniting  force 


VIII.]  SOLUTION-PRESSURE  149 

between  these  dissociated  ions  is  the  mutual  attraction  of  their 
+  and  -  charges.  Chlorides,  bromides,  and  iodides,  etc.,  of 
sodium,  potassium,  and  ammonium,  etc.,  in  dilute  solution — and 
decimolecular  solutions  such  as  we  find  it  convenient  to  use  in 
the  physiological  laboratory  are  in  this  connection  "  dilute  " — 
exist  in  this  active  state  of  ionisation  as  positively  charged 
kations  and  negatively  charged  anions.  I  said  this  active  state 
of  ionisation,  since  it  is  to  this  state  of  ionisation  that  their  chief 
chemical  and  physical  actions  are  due,  and  among  these  actions 
no  doubt  we  must  reckon  their  action  upon  living  matter. 

Now,  if  we  take  a  number  of  salts,  such  as  those  just  named, 
in  dilute  equimolecular  (or,  better,  in  isosmotic)  solution, 
and  systematically  compare  their  respective  effects  upon  some 
convenient  physiological  reaction  of  living  matter,  we  shall  find 
that  differences  of  the  kation  produce  far  greater  differences  of 
reaction  than  do  differences  of  the  anion. 

I  do  not  pretend  that  this  is  in  itself  any  proof  that  action 
and  action  currents  are  essentially  characterised  by  increased 
solution-pressure  and  actual  discharge  into  solution  of  electro- 
positive ions.  But  I  think  we  may  provisionally  conclude  that 
in  the  action  of  dilute  saline  solutions  upon  living  matter,  it  is 
the  electro-positive  kation  that  takes  the  lead,  acting  presum- 
ably in  the  sense  that  we  should  anticipate,  viz.,  increasing  the 
kationic  pressure  of  the  lymph  bath,  and  decreasing,  therefore, 
the  difference  between  that  pressure  and  the  kationic  solution- 
pressure  of  the  living  matter. 

The  state  of  things  under  the  influence  of  the  anode  must  be 
regarded  as  the  converse  to  that  just  pictured  as  obtaining  under 
that  of  the  kathode.  Anions  are  attracted,  kations  are  repelled  ; 
the  solution-pressure  of  the  latter  must  be  lowered,  and  the  sur- 
face of  living  matter  must  be  rendered  less  zincative,  less  easily 
made  to  discharge  kations  ;  and,  if  forced  to  such  discharge  by 
adequate  excitation,  manifesting  greater  effect  than  when  the 
initial  pressure  was  higher. 

The  post-anodic  action  current,  which  makes  its  appearance 
at  the  moment  of  cessation  of  an  exciting  (or  polarising) 
current,  is  very  easily  accounted  for.  The  kationic  solution- 
pressure,  depressed  under  the  influence  of  the  anode,  is  suddenly 


150  THE  SIGNS  OF  LIFE  [lect.  viii. 

released  when  that  influence  is  removed,  and  manifests  itself  in 
a  kationic  discharge  from  the  previously  anodic  surface.  Thus 
we  have  a  post-anodic  action  current  which  is  of  the  same  direc- 
tion as  that  of  the  previous  (polarising)  current. 

Blaze-currents — of  which  such  frequent  mention  has  been 
made  in  these  lectures — are  an  effect  of  local  intensifications  of 
electrolytic  solution-pressure — of  kationic  pressure  when  their 
direction  is  from  the  excited  spot ;  of  anionic  pressure  when 
their  direction  is  towards  the  excited  spot. 

This  is  hypothesis  which,  whether  or  no  it  "  explains "  all 
the  known  facts,  at  least  neither  contradicts  nor  obscures  them  ; 
it  seems  to  me  to  bring  them  under  a  common  denomination, 
and  to  invite  us  to  their  further  investigation.  Hypothesis  is 
the  mother  of  experiment. 


REFERENCES 

Engelmann. — "  Ueber  das  Vorkommen  und  die  Innervation  von  con- 
tractilen  Drlisenzellen  in  der  Froschhaut,"  Pflilger's  ArcMv,  iv.,  p.  i, 
1871. 

Engelmann. — "Ueber  die  electromotorischen  Krafte  der  Froschhaut, 
ihren  Sitz  und  ihre  Bedentung  fiir  die  Secretion,"  Pfliiget's  Archiv, 
iv.,  p.  321,  1871. 

Engelmann. — "Die  Hautdriisen  des  Frosches,''  Pfliiger's  Archzv,  v., 
p.  498,  1872,  and  vi.,  p.  97,  1872. 

MacDonald. — "The  Injury  Current  of  Nerve,"  Thompson  Yates  Labora- 
tories Report,  vol.  iv.,  part  ii.,  1902. 

BlEDERMANN. — Elektrophysiologie,  Jena,  1895  ("Action  of  Water  and  of 
Saline  Solutions  on  Mucosa  Currents,"  p.  401.) 

LOEB. — "  Physiologische  Untersuchungen  iieber  lonenwirkungen,"  P/?/i;^^r'.y 
Archiv,  Ixix.,  p.  i,  1898,  and  Ixxi.,  p.  457. 


APPENDIX 

The  Normal  Circuit — Galvanometer,  Coil,  Compensator,  Electrodes,  and  Keyboard — 
Photographic  Recording — Lippmann's  Capillary  Electrometer — Special  Keys — 
Units  of  Resistance  and  of  Conductance. 

In  a  physiological  laboratory  the  galvanometer  may  be  used  either 
for  special  electro-physiological  research,  or  in  the  course  of  research 
work  where  electro-physiology  is  of  secondary  interest — the  galvano- 
meter playing  the  part  of  a  balance,  to  indicate  physico-chemical 
differences  between  any  two  different  points. 

The  following  remarks  are  more  especially  directed  to  meet  this 
latter  case.  The  galvanometer  may  be  looked  upon  either  as  a 
manometer,  measuring  electrical  pressures  just  as  one  measures 
blood-pressure,  or  as  a  chemical  balance,  by  means  of  which  one 
can  compare  numerically  the  energy  values  of  physiological  pheno- 
mena capable  of  an  electrical  expression.  In  many  cases  it  will  be 
found  convenient,  or  even  necessary,  to  record  the  indications  of 
the  galvanometer  photographically. 

The  requisite  apparatus  consist  of:  (I)  the  galvanometer  ;  (II) 
the  compensator  ;  to  these  must  be  added  various  accessories  ;  (III) 
the  exciting  apparatus  ;  (IV)  the  electrodes  ;  and  (V)  the  keyboard, 
by  means  of  which  the  constituent  pieces  of  apparatus  will  be  con- 
nected together  to  form  what  may  be  termed  the  normal  circuit. 
(The  arrangement  for  taking  photographic  records  is  a  further 
accessory  described  below,  p.  156.) 

The  galvanometer. — The  style  of  instrument  matters  very  little 
so  long  as  its  sensibility  can  easily  be  ascertained  and  adjusted. 

The  delicacy  of  the  galvanometer  should  be  such  that  o.ooi  volt 
through  a  megohm  gives  a  deflection  of  10  cms.  at  a  distance  of 
2  metres.  Thus  a  deflection  of  i  cm.  corresponds  in  such  a  circuit 
to  a  current  of  io-^°  ampere, 

151 


152 


THE  SIGNS  OF  LIFE 


II  is  advisable  to  fit  up  a  galvanometer  once  and  for  all  in  one 
particular  place.  The  best  position  for  the  instrument,  and  one 
in  which  it  will  always  be  ready  to  work,  is  either  a  recess  or  small 
cupboard  built  in  the  thickness  of  a  perfectly  firm  wall.  Failing 
this,  a  firm  bracket  or  shelf,  not  connected  with  the  floor,  is  sufficient. 

Whether  the  instrument  is  being  used  for  purposes  of  demonstra- 
tion or  for  actual  measurement,  the  objective  method  must  be  used. 
This  consists  in  the  projection  of  a  beam  of  light  either  on  to  a  trans- 
parent and  graduated  scale  or  upon  a  photographic  plate.     The  most 


Fig.  56. — Normal  circuit  described  in  the  text.  (The  secondary  coil  is 
figured  as  if  for  direct  excitation  of  a  given  object,  IV.  Obviously,  if  we 
have  to  apply  indirect  excitation,  the  wires  are  removed  from  the  keyboard, 
and  the  plug  hole  is  filled  to  complete  the  keyboard  circuit.) 

convenient  light  for  either  purpose  is  the  image  of  the  filament  of  an 
incandescent  lamp.  When  photographic  records  are  required,  it  is 
very  desirable,  indeed  almost  indispensable,  to  work  with  two  galvano- 
meters in  series,  one  for  purposes  of  observation,  the  other  as  record- 
ing instrument. 

Calibration  of  the  galvanometer^  and  choice  of  a  convenient  scale. 
— The  deviations  of  the  same  galvanometer  have  not  always  a 
constant  value,  seeing  that  the  resistance  of  the  circuit  varies 
according  to  the  resistance  of  the  object  under  examination  and 
of  the  unpolarisable  electrodes. 

The  quickest  way  to  calibrate  a  galvanometer  is  to  observe  or 
photograph  the  deflection  of  the  spot  when  a  current   of  known 


APPENDIX 


153 


voltage  from  the  compensator  is  allowed  to  flow  in  the  circuit,  which 
must  be  of  known  resistance  (Fig.  59).  It  is  convenient  to  use  a 
carbon  megohm  for  calibration  {vide  infra  p.  169). 

In  those  cases  where  an  alteration  of  resistance  actually  occurs 
during  the  course  of  the  experiment,  the  value  of  the  standard  voltage 
must  be  taken  before  and  after. 

JSlote. — In  early  trial  experiments  the  deflections  obtained  will 
probably  be  too  large  to  be  kept  well  within  the  scale  hmits.  The 
best  way  to  obtain  a  readable  deflection  is  to  shunt  the  galvano- 
meter, thus  sending  only  a  convenient  fraction  of  the  total  current 
through  the  instrument. 

The  compensator  or  potentiometer  is  a  means  (i)  of  supplying  a 
standard  voltage,  and  (2)  of  compensating  and  so  measuring  P.D. 
currents  derived  from  the  'object  under  examination.  Further,  the 
compensating  current  affords  the  quickest  means  of  verifying  the 
integrity  of  the  general  circuit  and  of  the  galvanometer. 

In  its  simplest,  and  for  all  ordinary  purposes,  sufficiently  accurate 
form,  the  compensating  arrangement  consists  of  a  Leclanche  cell, 


Fig.  57. — To  illustrate  the  principle  on  which  a  compensator 
is  constructed  ;  with  a  battery  of  i  volt,  R  =  looo  ohms  and  ;'  =  I 
ohm,  the  P.D.  at  the  ends  +  and  -  would  be  approximately  ^^-^ 
volt;  the  same  P.D.  would  obtain  with  a  battery  of  1.4  volt  and 
R  =  1400  ohms.     Compensation  is  established  by  varying  r. 

joined  up  with  two  resistance-boxes,  which  act  as  numerator  and 
denominator  of  any  convenient  fraction  of  a  volt. 

Taking  the  voltage  of  the  cell  as  1.4,  and  the  resistance  (R)  of 
the  denominator  to  be  14,000  ohms,  than  the  resistance  (r)  of  the 
numerator  reckoned  in  ohms  will  give  a  voltage  in  ten-thousandths 
at  the  electrodes — e.g.^  if  r=\o  ohms,  the  voltage  obtained  =  .001 ; 
if  r  =  100,  voltage  =  .01 , 


154 


THE  SIGNS  OF  LIFE 


r  r 

of  the  voltasre   taken  is  not  -^  but  -5 


Note. — Obviously  this  yields  only  approximate  results,  since  the 
voltage  of  a  Leclanche  is  never  quite   1.4  volt,   and  the  fraction 

Further,  the   internal 

resistance  of  the  cell  is  not  taken  into  account.  The  method  is, 
however,  sufficiently  accurate,  seeing  that  the  principal  error  is 
a  constant  one  and  the  variable  error  is  negligible. 

In  actual  experiments  it  is  advisable  to  have  a  standard  com- 
pensator which  will  give  values  of  .01,  .001,  .0001  volt,  independently 
of  the  compensator  proper. 


Fig.  57  A. 


Compensator  to  deliver  TTTCinrth,  n^th,  or  iJ  u^h  of  a 
volt  from  a  Leclanche  cell  (of  1. 42  volt). 


The  comparison  between  experimental  deflections  and  the 
standard  deflection  of  known  external  voltage  is  not  calculated 
to  give  the  absolute  value  of  internal  E.M.F.  of  active  tissue.  The 
external  circuit  and  galvanometer  receive  only  a  fraction  of  the 
total  internal  electromotive  difference,  which  produces  current 
partly  through  the  internal  conducting  tissues,  partly  through  the 
external  (galvanometric)  arc.  Moreover,  the  time -relations  of 
physiological  action  are  generally  such  that  internal  effects  of 
brief  duration  produce  small  external  effects  that  cannot  be 
standardised  by  a  prolonged  external  voltage. 

Thus,  e.g.^i  a  nervous  impulse  with  a  duration  of  say  0.005  sec. 
might,  on  a  given  instrument,  produce  the  same  deflection  as  a 
constant  current  from  an  E.M.F.  of  o.ooi  volt,  but  this  would 
not  indicate  electromotive  value  of  the  nervous  impulse.  A  closer 
approximation  would  be  arrived  at  by  making  the  comparison  with 


APPENDIX  155 

an  external  voltage  effective  for  only  0.005  sec.  ;  in  this  manner 
Gotch  and  Burch  have  assigned  0.03  volt  as  the  electromotive  value 
of  a  single  nervous  impulse.  And  this  is  not  yet  a  true  value,  by 
reason  of  the  internal  derivation  alluded  to  above. 

The  principal  object  of  a  standard  voltage  at  the  commence- 
ment and  termination  of  experiment  is  (i)  to  indicate  that  the 
resistance  has  or  has  not  sensibly  altered  during  experiment  ;  and 
(2)  to  indicate  the  sensibility  of  instruments  employed.  It  does 
not  afford  in  itself  satisfactory  data  for  a  comparison  between 
electromotive  values  of  response  of  different  tissues,  and  it  is  only 
with  reservation  {i.e.^  after  control  of  altered  resistance  and  altered 
duration  of  action)  that  it  can  be  utilised  for  the  detection  and 
estimation  of  altered  electromotive  values  during  any  one  obser- 
vation. 

Bearing  these  reservations  in  mind,  we  may,  however,  be 
allowed  to  speak  of  the  "  voltage "  of  an  injury  current  as 
"measured"  by  that  of  a  compensation  current,*  and  to  indicate 
by  reference  to  standard  deflections  the  scale  of  voltage  in  which 
blaze-currents  are  externally  manifested. 

The  excitmg  apparatus. — In  the  great  proportion  of  experiments 
the  du  Bois-Reymond  induction  coil  (Berne  model)  is  used.  This 
coil  has  its  graduation  in  arithmetical  progression. 

In  those  experiments  where  it  is  necessary  to  estimate  the 
quantity  or  energy  of  the  discharge,  a  condenser  must  be  used. 
In  either  case  there  are  two  possible  methods  of  excitation  : — 
(i)  the  excitation  is  sent  through  object  and  galvanometer  in 
series,  and  (2)  the  galvanometer  is  short-circuited  during  excita- 
tion, and  put  into  circuit  after  a  given  short  interval  of  time. 

Electrodes. — It  is  absolutely  essential  that  the  electrodes  should 
be  unpolarisable.  Du  Bois  -  Reymond's  combination  (zinc  and 
sulphate  of  zinc)  has,  in  my  experience,  given  better  electrodes 
than  those  recently  introduced — e.g..,  silver  and  silver  chloride, 
or  mercury  and  calomel. 

Keyboard. — In  the  constant  use  of  a  galvanometer  as  a  measuring 
instrument,  the  circuit  should  be  set  up  in  such  a  manner  that  the 
direction  of  exciting  and  reaction  currents  may  be  quickly  determined. 

*  The  instrument  by  which  this  is  done  is  a  compensator  ;  it  is  not  strictly  speaking 
?i  potentiometer. 


156  THE  SIGNS  OF  LIFE 

The  simplest  way  of  obtaining  this  arrangement  is  to  have  a 
keyboard  with  several  pairs  of  terminals,  to  which  are  connected 
the  various  parts  of  apparatus,  making  up  what  has  already  been 
called  the  normal  circuit.  Each  particular  piece  of  apparatus  is 
controlled  by  a  plug,  opening  or  closing  the  interval  between  the 
two  terminals  to  which  each  pair  of  wires  is  connected.  Two 
commutators,  one  in  the  exciting  circuit  and  the  other  in  the 
compensator  circuit,  allow  the  current  to  be  sent  in  the  direction 
desired.  An  ordinary  key  interrupts  the  principal  circuit  of  the 
compensator. 

Note.  —  It  much  simplifies  matters  to  arrange  the  circuit 
permanently,  or  at  least  at  the  beginning  of  each  experiment,  so 
that  a  positive  or  negative  current  may  be  in  conventional 
directions,  i.e.,  positive  to  the  right  and  negative  to  the  left. 
The  quickest  way  of  determining  the  direction  of  a  current  is 
to  touch  one  of  the  terminals  with  a  piece  of  metal  {e.g.,  zinc) 
held  in  one  hand,  while  a  finger  of  the  other  hand  makes  contact 
with  the  other  terminal.  The  terminal  touched  by  the  zinc  "  pulls  " 
through  the  galvanometer,  and  if  the  previous  deflection  has  been 
in  the  same  or  in  the  opposite  direction,  we  know  that  the  spot 
in  connection  with  the  same  terminal  was  then  zincative  or  counter- 
zincative,  i.e.,  electro-positive  or  electro-negative. 

Photogaphic  recording. — If  necessary,  it  is  possible  to  photograph 
and  to  take  readings  at  one  and  the  same  time.  To  this  end  the 
transparent  scale  must  be  replaced  by  a  vertical  opaque  screen, 
with  a  narrow  horizontal  slit,  behind  which  a  photographic  plate 
is  let  down  by  clockwork. 

The  use  of  two  galvanometers  in  series  so  simplifies  matters, 
however,  that  it  is  preferable  to  use  a  second  instrument  for  taking 
graphic  records.  One  of  the  galvanometers  stands  in  the  laboratory, 
with  its  transparent  scale  in  front  of  the  observer,  while  the  second 
is  some  distance  away  in  a  dark  (and  non-vibrating)  room.  The 
former  exhibits  and  the  latter  registers  the  currents  under  obser- 
vation. 

The  graduation  of  the  recording  galvanometer  should  be  to  a 
smaller  scale  than  that  of  the  indicating  galvanometer.  A  con- 
venient relation  between  the  two  scales  is  i  to  lo,  so  that  each 
centimetre  deflection  of  the  indicator  is  represented  by  a  millimetre 
on  the  recorder.     The  relation  is,  if  necessary,  adjusted  by  shunting 


APPENDIX 


15T 


one  or  other  of  the  two  galvanometers  ;  and  once  estabhshed,  we 
may,  if  desired  further,  shunt  both  galvanometers,  so  as  to  reduce 
both  deflections  in  the  same  proportion.  For  this  reduction,  the 
common  shunt  is  to  be  connected  with  the  terminals  on  each  side 
of  plug  No.  I. 


Fig.  58. — Galvanograph, 

The  most  convenient  arrangement  of  the  two  galvanometers  is 
shown  in  Fig.  58,  in  which  G;^  is  the  indicator  and  G^  the  recorder. 
The  two  galvanometers  are  controlled  simultaneously  by  plug  No.  i, 
separately  and  individually  by  plugs  No.  5  and  6  of  a  secondary  key- 
board. We  are  therefore  able  to  adjust  compensation  and  make 
any  necessary  preliminary  adjustments  with  the  photographing 
galvanometer  short-circuited  at  No.  6,  and  therefore  undisturbed 
by  manipulations  in  the  remainder  of  circuit,  where  we  are  guided 
by  the  indicating  galvanometer.  For  an  observation  of  any  duration, 
both  galvanometers  are  in  circuit  and  simultaneously  controlled  by 
plug  No.  I,  and  the  general  progress  of  a  record  on  G2  in  the  dark 
room,  can  be  followed  on  the  scale  of  G^  placed  in  front  of  the  work- 
table. 

The  accessory  apparatus,  containing  the  sensitive  plate,  consists 
in  a  box,  |  metre  in  height,  which  carries  the  scale,  and  the  horizontal 
slit,  I  mm.  in  width,  upon  its  anterior  surface.     The  plate,  which  is 


158 


THE  SIGNS  OF  LIFE 


Fig.  59. — Photographic  record  of  the  galvanometric  deflections 
in  +  and  -  directions,  caused  by  (approximate)  voltages  of  o.oi, 
0.02,  0.03,  0.04,  and  again  0.03,  through  a  circuit  of  (approximately) 
one  Megohm  (  =  1000000  ohms). 


0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

Q 

0 

0 

0 

(vr 

^j- 

T 

■0" 

vcT 

K- 

QT 

cr 

cr 

Fig.  60. — Photographic  record  of  the  deflections  caused  by 
break,  induction  shocks  of  a  Berne  coil.     Two  trials  at  each  strength. 


APPENDIX 


159 


in  a  photographic  carrier  suspended  by  a  thread  from  a  wheel  revolv- 
ing by  clockwork,  descends  vertically.  The  deflections  of  the 
galvanometer  spot  are  recorded  laterally  upon  the  line  of  the 
horizontal  slit.  An  electric  bell  gives  warning  when  the  plate  has 
completed  its  descent.  If  necessary,  a  chronograph,  and  a  signal 
to  mark  the  beginning  and  close  of  excitation,  are  easily  added 
when  required. 


Before. 


^looo  voLb. 

Fig.  6i. — Response  of  an  oxydised  copper  plate,  illuminated 
for  seven  seconds  at  one  minute  intervals.  A  prolonged  illumination 
was  made  in  the  middle  of  the  series  to  see  whether  any  sign  of  ex- 
penditure would  be  elicited.  (The  first  deflection  by  ttjV's  ^ol' 
turned  into  circuit  exhibits  signs  of  ordinary  polarisation.) 


iJuLLLLLlill 


Before. 


ILLumin. 


Afber. 


Fig.  62. — Similar  observation  on  a  chlorinated  silver  plate.  In 
consequence  of  prolonged  illumination  there  is  well-marked  evidence 
of  alteration. 


Speed  of  registration. — By  reason  of  the  inertia  of  the  suspended 
magnets  and  mirror  of  the  galvanometer,  we  must  content  ourselves 
with  registering  phenomena  that  are,  comparatively  speaking,  pro- 
longed, or  repeated  at  regular  intervals.  The  method  is  not  adapted 
to  record  phenomena  that  require  a  speed  of  recording  surface 
greater  than  5  mm.  per  second.  It  is  best  adapted  to  the  recording 
of  phenomena  of  long  duration,  or  to  reactions  that  are  repeated 


160 


THE  SIGNS  OF  LIFE 


at  regular  intervals.  In  this  class  of  observations,  a  speed  of  2^  to 
5  mm.  per  minute  is  usually  sufficient.  The  "  lost  time  "  of  nerve- 
skin  reaction  is  a  good  instance  of  a  phenomenon  fitted  for  the 
galvanometric  record,  e.g.^  Figs.  28  and  43. 

It  is  convenient  to  adopt  a  standard  size  of  recording  plate  ;  the 
"quarter  plate"  in  England,  and  the  9  by  12  on  the  Continent, 
answer  all  ordinary  purposes.  These  dimensions  enable  us  to 
record  a  series  of  deflections  with  an  amplitude  varying  from 
I  to  5  cm.,  and  a  length  of  at  least  10  cm.      The   speeds  named 


Fig.  63. — Galvanograph  and  Railway  Myograph. 

give  records  lasting  40  and  20  minutes  ;  5  mm.  per  second  gives 
a  20  seconds  record.  For  speeds  above  5  mm.  per  second  a  record- 
ing electrometer  should  be  used. 

Simultaneous  records. — In  certain  cases  it  is  desirable  to  obtain 
the  simultaneous  record  of  a  series  of  electrical  reactions  and  of  the 
corresponding  series  of  muscular  contractions. 

For  this  purpose,  a  truck  carrying  a  smoked  plate,  and  con- 
nected with  the  suspended  carrier  that  holds  the  photographic 
plate,  is  added  to  the  apparatus.  The  thread  by  which  the  carrier 
is  suspended  passes  round  the  axis  of  the  motor  and  over  two  small 
pulleys,   and    is    fastened    to    the    carrier   of    the    smoked    plate, 


APPENDIX 


161 


which  accordingly  moves  in  a  horizontal  direction,  corresponding 
with  the  vertical  descent  of  the  sensitive  plate.  In  this  manner  a 
simultaneous  record  may  be  obtained,  e.g.^  of  a  series  of  muscular 
contractions  along  with  the  negative  variations  of  the  muscle- 
current  ;  or,  again,  of  contraction  and  heat  (by  means  of  a  thermo- 
galvanometer)  ;  or  of  the  contractions  of  a  muscle  and  the  negative 
variations  of  its  nerve  ;  etc.,  etc. 


Fig.  64. 

In  the  Physiological  Laboratory  of  the  University  of  London 
the  apparatus  described  above  is  disposed  according  to  the  following 
plan,  so  as  to  afford  two  complete  working  tables  with  two  pairs  of 
galvanometers  and  accessory  apparatus  : — 

The  galvanometers  G^  to  G5  are  placed  on  brackets  along  one 

L 


162  THE  SIGNS  OF  LIFE 

side  of  the  general  laboratory  as  figured.  (The  extra  galvanometer, 
Gg  is  a  separate  low-resistance  instrument,  for  use  with  either  table^ 
to  give  thermo-electric  readings  of  temperature  ;  it  is  worked  by  a 
constantan-iron  junction,  the  varying  E.M.F.  of  which  is  balanced 
by  compensation  ;  the  compensator  is  graduated  so  that  a  known 
length  has  a  known  temperature  value.) 

Each  pair  of  galvanometers,  G^  and  Gg,  G^  and  G5  is  intended  to 
be  used  as  described  above  ;  for  ordinary  work,  only  the  observation 
galvanometer  Gg,  or  G^,  is  used  ;  when  a  phenomenon  deserving  to 
be  recorded  presents  itself,  the  recording  galvanometer  G;^,  or  Gg,  is 
unplugged,  and  the  recording  surface  is  set  in  motion. 

The  apparatus  is  thus  utilised  in  the  general  laboratory  without 
suffering  any  disturbance  from  other  work  in  progress  in  the  same 
room. 

Lippmami' s  Capillary  Electrometer^  like  the  galvanometer,  can 
be  used  (i)  as  a  refined  instrument  of  research  for  the  special 
purposes  of  electro-physiology,  in  which  case  its  photographed 
indications  must  be  mathematically  analysed  ;  or  (2)  as  an  ordinary 
laboratory  instrument  for  the  summary  inspection  and  the  con- 
venient demonstration  of  electrical  changes  that  are  too  brief  or 
in  too  rapid  succession  to  be  readable  by  galvanometer — e.g.^  the 
electrical  changes  accompanying  the  beat  of  the  heart.  By  means 
of  very  simple  recording  apparatus,  the  value  of  the  electrometer 
as  an  ordinary  instrument  of  inspection  and  demonstration  is  greatly 
enhanced.  In  this  laboratory  a  capillary  electrometer  is  currently 
used  in  place  of  a  demonstrating  galvanometer.  The  image  of 
the  capillary  in  the  projection  microscope,  with  \  ^o  to  objective, 
is  first  thrown  upon  a  transparent  screen,  where  the  movements 
of  the  column  of  mercury  are  shown.  An  opaque  screen  with  a 
narrow  vertical  slit,  behind  which  a  vertical  photographic  plate 
travels  horizontally,  is  then  placed  on  the  lecture-table,  so  as  to 
receive  the  image  of  the  moving  column  of  mercury,  which  is  thus 
photographed.  And  lastly,  the  developed  photograph  is  exhibited 
in  the  ordinary  projection-lantern.  Thus  the  record  of  move- 
ments that  have  just  been  seen,  is  exhibited  and  examined.  In 
this  manner  there  is  no  difficulty  in  demonstrating  in  the  course 
of  a  quarter  of  an  hour  ist,  the  electroscopic  indications  of,  e.g.., 
a  frog's  heart ;  2nd,  the  photographed  records  of  such  indications. 

The  diameter  of  the  capillary  column  of  mercury  is,  e.g..^  25  /a. 


APPENDIX 


163 


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164 


THE  SIGNS  OF  LIFE 


On  the  screen,  at  a  distance  of  8  to  12  feet  the  magnification  of 
the  image  given  by  the  -^^  inch  objective  is  1000  to  1500  diameters, 
z'.e.^  the  column  has  an  apparent  diameter  of  25  to  37.5  mm. — an 
inch  to  an  inch  and  a  half.  On  the  photographic  plate,  at  a 
distance  of  2  feet,  the  apparent  diameter  is  upwards  of  6  mm. — 
far  more  than  is  sufficient  to  certainly  cover  the  vertical  slit,  the 
breadth  of  which  is  less  than  ^  mm.  For  the  frog's  heart,  a  lower 
magnification  is  generally  sufficient.  For  the  human  heart,  as 
high  a  magnification  as  practicable  should  be  employed. 


o  Sec. 


•6 


miLUvoLt 
0-5 


Fig.  66. — An  electrometer-curve  of  the  electrical  variation  of  the  human  heart ; 
the  values  calculated  from  the  record  of  the  mercury  level  are  given  as  a  dotted  line. 
(From  Einthoven,  Pfliigers  Arckiv,  vol.  60,  1895.) 


The  principle  upon  which  electrometer  values  are  obtained  from 
such  electroscopic  records  is  readily  illustrated  by  demonstrating  the 


APPENDIX 


165 


excursions  and  records  caused  by  different  voltages  acting  for  equal 
times,  and  by  a  given  voltage  acting  for  different  times. 

The  voltage  actually  indicated  by  any  given  curve  or  portion  of 
a  curve  is  most  readily  ascertained  by  superposing  the  record  upon 
the  record  of  a  "  normal  curve,"  i.e.^  of  the  curve  described  by  a 
known  constant  P.D.  taken  under  similar  conditions.  The  two 
plates  are  slipped  over  each  other,  with  abscissae  kept  parallel  until 
portions  of  the  curve  under  examination  coincide  with  portions  of 
the  normal  curve  at  known  voltage.  Such  coinciding  parts  are 
equipotential,  so  that  the  value  on  the  normal  curve  gives  the  value 
on  the  curve  under  inspection. 

For  the  more  minute  analysis  of  electrometric  curves,  the  student 
should  consult  the  papers  of  Burch,  Einthoven,  and  Garten.  In 
many  instances  the  calculated  curve  appears  very  different  from  the 
original  record  of  the  curve  described  by  the  mercury  column,  e.g.^ 
Fig.  66. 

Object. 


Fig.  67. — The  primary  circuit  of  the  inductorium  is  completed  through  the  pools 
pp.  The  galvanometer  is  short-circuited  through  the  other  pair  of  pools  G  G.  The 
level  of  mercury  in  the  lateral  pool,  and  the  length  of  the  semicircular  wires,  are 
adjusted  so  that  circuit  is  completed  at  G  G  (i.e.,  the  galvanometer  is  short-circuited) 
before  circuit  is  completed  at  //.  On  releasing  the  commutator  cradle  the  weight,  W, 
lifts  the  two  wires  from  the  mercury,  breaking  first  the  primary  circuit,  and  subse- 
quently the  galvanometer  short-circuit.     The  time  of  transfer  is  thus  kept  constant. 

Keys. — For  the  study  of  blaze-currents,  occasional  use  has  been 
made  of  two  special  keys,  modified  from  the  well-known  model  of 
the  Pohl's  commutator,  for  the  purpose  of  automatically  (i)  breaking 


166 


THE  SIGNS  OF  LIFE 


the  primary  circuit,  and  (2)   opening  the    galvanometer  circuit,  in 
quick  and  regular  succession. 

This  is  very  simply  effected  in  the  first  of  these  keys  by  making 


B     C    A 

Objecb. ' 

Fig.  68. — A  B  C  Key.  The  primary  circuit  of  the  inductorium  is  completed 
through  the  pools  /  /.  Connection  between  G  G  short-circuits  the  galvanometer. 
Of  the  three  pools  in  the  centre  of  the  key,  the  middle  is  connected  to  A,  via  the 
keyboard  and  galvanometer,  the  pool  under  W  to  C,  and  the  remaining  pool  to  B. 
The  three  arms  of  the  rocker  are  of  unequal  length,  that  connecting  G  G  being  a 
little  longer  than  the  centre  arm,  and  this  again  longer  than  the  connection  between 
/  /.  On  rocking  the  arms  to  the  left,  and  then  letting  go  the  weight,  the  following 
events  take  place  in  order  : — 

{a)  The  circuit//  is  broken,  and  an  induction  current  passes  through  B  A. 
((5)     ,,         ,,     B  A  is  broken. 
(c)      ,,         „     A  C  is  made, 

{jl)     ,,  ,,     G  G  is  broken,  and  any  potential  difference  between  A  and  C 

acts  upon  the  galvanometer. 

Thus  the  in  iuction  shock  caused  by  breaking  p  p  passes  through  A  B,  A  is  then 
connected  to  C,  and  not  till  then  is  the  galvanometer  short-circuit  G  G  broken,  and 
the  current  from  A  C  allowed  to  pass.  To  take  the  current  from  B  C,  the  connections 
A  and  B  are  transposed. 


the  curved  wire    in  the  galvanometer  short-circuit  a  little  longer 
than  that  in  the  primary  circuit,   so  that  the  break  shock   takes 


APPENDIX 


167 


place  a  little  before  the  galvanometer  is  un-short-circuited.  The 
removal  of  the  two  curved  wires  from  their  respective  mercury 
pools  is  maintained  at  a  regular  interval  by  the  use  of  a  weight. 
This  key  is  used  to  demonstrate  the  total  effect  between  two  points, 
A  B,  after  excitation  of  these  same  points. 

The  second  key  is  a  little  more  complicated,  and  serves  to 
demonstrate  a  partial  effect  A  C  or  B  C  after  excitation  of  two 
points  A  B. 

Units  of  Resistance  and  of  Conductance* — The  units  of  resistance 
are  the  ohm  and  the  megohm  (=1,000,000  ohms).  The  corres- 
ponding units  of  conductance  are  the  mho  and  the  gemmho,  which 
are  the  reciprocals  of  the  ohm  and  megohm. 

A  substance  having  a  resistance  of  one  megohm  (i2)  has  a  con- 
ductance of  I  gemmho  or  i  y. 

^  ^  =  i- 

The  conductances  of,  e.g.^  the  skin  in  the  experiment  illustrated 
by  Fig.  50  are  accordingly  : — 


*  I  am  indebted  to  Professor  Ayrton  for  the  suggestion  of  the  reciprocal  megohm 
as  a  convenient  unit  of  conductance,  and  for  the  further  suggestion  of  "  gemmho  "  or 
7  as  its  convenient  name  and  symbol,  thus  utilising  Lord  Kelvin's  proposal  to  take 
resistance  names  written  backwards  to  denote  their  conductance  reciprocals.  Kohl- 
rausch's  unit  of  conductivity  i  /c  is  the  same  as  Kelvin's  "  mho,"  and  is  equal  to 
1,000,000  7.  I  have  also  to  acknowledge  the  kind  assistance  of  Dr  T.  Martin 
Lowry  in  connection  with  conductivity  measurements. 


168 


THE  SIGNS  OF  LIFE 


From  which  it  is  evident  that  where  the  resistance  of  the  object 
examined  is  great  as  compared  with  the  resistance  of  the  galvano- 
meter and  electrodes  (20,000  ohms  in  this  instance),  we  may  regard 
alterations  of  deflection  as  indicating  alterations  of  conductance. 
Whereas,  if  the  resistance  of  the  object  be  relatively  small,  we  must 
calculate  the  conductance  after  subtracting  from  the  total  resistance 
in  circuit  the  resistance  of  the  galvanometer  and  electrodes. 

For  many  purposes — e.g.^  for  comparing  the  resistance  (or  con- 
ductance) of  various  objects — it  will  evidently  be  necessary  to  reduce 
our  results  to  a  common  denomination,  i.e.^  to  the  resistance  (or 
conductance)  of  a  cube  of  i  centimetre.  Thus,  e.g.^  a  stem  10  cm. 
long  with  a  sectional  area  of  10  square  millimetres,  having  a 
resistance   of  say    200,000   ohms    (  =  a   conductance    of  57)    has   a 

resistivity  =   and  a  conductivity  =  ^  x  10  x  10.    The  reduction 

■^10x10  ^      ^ 

to  the  cube  of  i  cm.  is  in  conformity  with  the  practice  of  modern 

physical  chemistry.    The  conductivity  of  i  megohm,  or  i  y,  =  i.io~^" 

C.G.S.  unit,  that  of  i  ohm,  or  lo^y  being  i.io~^. 

Electrolytes  in  general  are  increased  in  conductivity  by  rise  of 

temperature,  the  co-efficient  of  increase  being  approximately  2  per 

cent,  per  degree. 


Resistivity 
(in  ohms) 


Conductivity 

(in  reciprocal 

megohms) 


Mercury         ...... 

Sulphuric  acid,  30  %  at  40°   . 

Sodium  chloride,  sat.  sol.  at  18°,  26.4% 

,,  ,,  mo),  sol.  at  18°,  5.62  % 

m 

„  „  —    sol.  at  18°,  0.58  % 

Sea-water,  a.t  i^'"  . 

Seaweeds       ..... 


0.000,094 
I 

4.627 
1345 


Urine    ...... 

Blood  serum  .... 

Defibrinated  blood 

Muscle  and  Nerve  (longitudinall}') 


Grape-juice   . 
Vegetables  and  Fruits  . 
Ordinary  tap-water 
Ordinary  distilled  water 
Good  ,,  ,, 

Kohlrausch  „ 


50 
125 
250 
200 

500 
2,000 
2,500 

I0O,CO0 

1,000,000 
25,000,000 


10,630,000,000 

1,000,000 

216,100 

74,400 
9-250 

50,000 
12,500 

20,000 
8,000 
4,000 
5,000 

2,000 

500 

400 

10 

I 

0.04 


APPENDIX  169 

Measurements  of  resistance  (and  of  conductance)  are  best  taken 
by  means  of  a  Wheatstone  bridge,  preferably  by  Kohlrausch's  method, 
but  for  many  purposes  where  polarisation  of  electrodes  and  of  tissue 
may  be  disregarded,  it  is  convenient  and  sufficient  to  estimate  con- 
ductance directly  from  the  galvanometric  deflection.  In  the  case 
of  plants  the  resistance  is  generally  so  great  that  it  is  allowable  to 
disregard  that  of  the  galvanometer  and  electrodes,  and  to  at  once 
express  deflections  in  terms  of  conductance.  A  carbon  megohm 
(=1,000,000  ohms)  attached  to  the  keyboard  is  a  convenient 
standard  of  reference,  giving  at  once  on  the  scale  or  photograph 
the  value  of  our  unit  of  conductance,  i  y. 

Correction  for  the  resistance  of  the  galvanometer  and  electrodes 
is  to  be  made,  when  required,  as  follows  : — 

Let  r^  and  d^  be  the  resistance  of  the  galvanometer  +  megohm, 
and  the  deflection  by  any  convenient  voltage. 

r^  and  ^o  ^^  resistance  of  the  galvanometer  +  electrodes,  and 
the  deflection  by  the  same  voltage  (practically  we  must  take  y^th 
or  xTO^h  that  voltage  and  multiply  by  10  or  100). 

rg  and  d^  the  resistance  of  the  galvanometer  +  electrodes-}- object 
of  experiment,  and  the  deflection  by  the  same  voltage. 

The  required  resistance,  1\^  of  the  object  examined  =  r.^  -  7'^, 

and  smce         --L    =    — ^      and  — ^   =    ~f 
r.,  d^  7-3  d^ 

1  •      1         •  ,  ^'^d■,  i\d. 

the  required  resistance  r,    =   -V^    -   -\^ 

"3  "2 

_    i\d-^{d^-  d-^) 
d^d^ 

and  the  corresponding  conductance   =   — .  ,^,  ^ — 7-^. 

i\d^{d-2-d^ 

If  the  galvanometer  resistance  is  known,  it  is,  although  convenient, 
not  necessary  to  take  a  megohm  into  circuit. 

Kohlrausdi' s  method  is  used  in  this  laboratory  for  the  rapid 
testing  of  distilled  water,  of  dilute  saline  solutions,  and  of  blood, 
serum,  urine,  etc. 

The  electrodes  (of  platinised  platinum)  are  adjusted  to  a  suitable 
''resistance  capacity"  (about  -^  for  water,  i  for  dilute  sahne,  serum, 


170  THE  SIGNS  OF  LIFE 

and  blood,  and  lo  for  solutions  of  higher  conductivity)  so  that  the 

resistance  under  observation  shall  fall  between  the  limits  of  loo  and 

looo  ohms.  The  electrodes,  forming  the;varmof  aWheatstonebridge, 

are  plunged  into  the  fluid  under  examination  ;  a  telephone  is  in  the 

bridge  in  place  of  a  galvanometer  ;  the  testing  currents  come  from  a 

small  induction  coil,  and  the  silence  point  (or  its  equal  "  to  much  " 

and  "  too  little  ")  is  sought  for  by  alteration  of  the  variable  resistance. 

Readings  of  resistance  are  thus  easily  obtained  within  an  error  of 

±  I  per  loo,  with  the  normal  temperature  =  i8°.     A  correction  of 

±  2  per  ICO  of  the  reading  is  to  be  made  per  ±  i°. 

rpii         ,      •/-  7     -•   -J  Resistance  Capacity 

i  he  specific  conductivity    =    --^ =-^^ — f — 

Ubserved  Resistance 

The  resistance  capacity  of  a  given  pair  of  electrodes  in  a  given 
vessel  is  ascertained  by  taking  a  measurement  of  resistance  through 
a  standard  solution  of  known  conductivity.  E.g.^  a  pair  of  electrodes 
in  decinormal  KCl  at  i8°  is  found  to  have  a  resistance  —  200  ohms. 
The  resistance  capacity  =  200  x  o.oiiiq  =  2.238  [Resistance  x 
Conductivity  =  Capacity'). 

With  the  same  pair  of  electrodes  the  resistance  of  a  specimen 
of  serum  is  found  to  be   320  ohms.      Its  specific   conductivity   = 

^      =   0.006994  mho  or  6994  7. 
320 

The    necessary   data   are    given    in    Kohlrausch    and    Holborn's 

tables,  from  which  the  following  useful  empirical  rule  is  taken  : — 

For  weak  saline  solutions  (—  and  under)  the  specific  conduc- 
tivity (in  mhos)  x  10  =  the  number  of  gramequivalents  per  litre, 
and  -  the  specific  conductivity  x  molecular  weight  =  the  percentage 
of  salt  in  solution. 


REFERENCES 


LiPPMANN. — "  Capillary  Electrometer,"  Coniptcs  Rendus  de  P Academic  des 

Sciences.,  p.  1407,  1873. 
Marey  and  Lippmann. — "  Electrometer  Records,"  Coinptes  Rendus.,  p.  278, 

1876. 
Burdon-Sanderson  and  Page. — "  On  the  Electrical  Phenomena  of  the 

Excitatory  Process  in  the  Heart  of  the  Frog  and  of  the  Tortoise,  as 

investigated  Photographically,"  Journal  of  Physiology.,  vol.  iv.  p.  327, 

1883. 


APPENDIX  171 

BURCH. — "  On  the  Time  Relation  of  the  Excursions  of  the  Capillary  Electro- 
meter," Phil.  Trans.  Roy.  Soc.^  vol.  183,  p.  8r,  1892  ;  Proceedings  Roy.  Soc, 
vol.  60,  p.  329,  1896. 

EiNTHOVEN. — "  Lippmann's  Capillar-Electrometer  zur  Messung  Schnell- 
wechselnder  Potentialunterschiede,"  Pfliiger's  Archiv,  Bd.  56,  p.  528, 
1894  ;  Bd.  60,  p.  91,  1895  ;  Bd.  79,  p.  i,  1900. 

Hermann.  —  "  Das  Capillar  -  Electrometer  und  die  Actionsstrome  des 
Muskels,"  Pfliiger's  Archiv,  Bd.  63,  p.  440,  1896. 

Garten. — "  Ueber  ein  einfaches  Verfahren  zur  Ausmessung  der  Capil- 
larelektrometer-Curven,"  Pfliiger's  Archiv,  Bd.  89,  p.  613,  1902. 

KOHLRAUSCH  UND  HOLBORN. — Leitverviogen  der  Elektrolyte.  Leipzig, 
1898. 

E.  Cohen. —  Vortrdge  fiir  Artzfe  iiber  Physikalisch  Cheinie.      Leipzig,  1891. 

Whetham. — Solutio7i  atid  Electrolysis.  Cambridge,  1895.  (New  edition, 
1902.) 

R.  HoBER. — Physikalische  Cheniie  der  Zelle  und  der  Geivebe.     Leipzig,  1902. 


INDEX 


ABC    METHOD,   69,    87,    94,    95,    107, 

112,  115,  133,  145- 
After  effects  in  eyeball,  43,  45. 
Aim  of  lectures,  i. 
Anaesthetics,  action  of,  38. 
Anodic  (post)  action  currents,  y^)- 
Anomalous  polarisation,  130. 
Antidrome  currents,  47. 
Atropin  on  skin,  65. 

Back  on  action  of  mercuric  chloride, 

83. 
Bean-radicle,    mechanical    excitation 

(fig.  6),  15. 

Bernard  on  analysis  and  synthesis,  35. 

Biedermann  on  anodic  and  kathodic 
currents,  91,  108  ;  on  mucous  mem- 
branes, 66,  III,  138. 

Blaze  (manipulation-)  in  eyeball,  25;  in 
skin,  60  ;  currents,  49,  53,  106,  143  ; 
definition  of,  73 ;  similarity  with 
discharge,  74  ;  anodic  and  kathodic, 
no. 

Blaze,  partial  and  total,  95. 

Brown,  Horace,  on  seeds,  6. 

Burdon-Sandersoft  on  Dionsea,  12. 

Carbon  dioxide,  action  of,  39,  74. 
Cause,  its  relation  to  effect,  35,  36,  52. 
Chemical  change,  3  ;  methods,  6. 
Chloroform,  action  of,  39. 
Coil,  induction,  description  of,  155. 
173 


Colours,  complementary,  35. 
Compensator,  description  of,  153. 
Concentration  currents,   135,   137,  139 

(fig.  55),  143. 
Conductance,  167,  169. 
Conductivity,  168. 
Conductivity  in  eyeball,  44. 
Congelation  blaze,  119. 
Copperplate,   effect   of    light    on,    29, 

159  (fig.  61). 
Crystalline  lens,  blaze-currents  of,  56. 
Current  in  retina,  10  ;  initial  (in  retina), 

24  ;  of  darkness,  27;  norinal  (in  skin); 

60,   104  ;   of  action,   73  ;  plant,   94  ; 

accidental,      103  ;     Quinke's,      133  ; 

concentration,  135,  137,  140  (fig.  55) ; 

density,  113  ;  evaporation,  136. 

Darkness,  current  of,  27. 

Dewar  and  MacKendrick  on  latency 
in  eyeball,  28. 

Discharge  of  electrical  organ,  73,  76? 
78  ;  skin,  82. 

Du  Bois-Reymond,  negative  varia- 
tion, 14,  18 ;  on  positive  polarisa- 
tion, 73,  89  ;  on  electromotive  pheno- 
mena, 74,  76  ;  on  torpedo,  78,  79  ; 
"  Willkiirversuch,"  121  (fig.  52);  in- 
duction coil,  154. 

Durig  on  surviving  skins,  141. 

Effect,  its  relation  to  cause,  35,  36,  ■^7, 


174 


INDEX 


Electrical  fishes,  75  ;  organs,  76 ;  organs 

of  torpedo,  78. 
Electrocution  of  eyeball,  49. 
Electrodes,  155  ;  fallacy  of,   129,  130, 

^33- 

Electrometer,  capillary,  29,  100,  162. 

Engehna7in  and  Grijns  on  action  of 
anaesthetics,  39 ;  Engebnann  on 
nerve-skin,  61,  63  (fig.  29),  65  ;  on 
skin,  138. 

Ether,  action  of,  39. 

Evaporation  current,  136. 

Excitability  of  vegetable  protoplasm, 
12,  19. 

Excitation,  indirect  (of  skin),  60,  65  ; 
direct  (of  skin),  65  ;  of  cat's  pad,  10 1  ; 
summating  effect  of,  68  (fig.  31); 
effect  of,  direct  or  indirect,  83. 

Eyeball,  currents  in,  10,  11,  12,  19,  25  ; 
as  an  optical  instrument,  22  ;  electri- 
cal effects  of  light  and  of  electrical 
excitation,  23  (fig.  8),  55  ;  normal 
response  in,  27  ;  three  types  (fig.  13), 
30,  50;  massage  of,  31 ;  tetanisation 
of,  42;  electrocution  of,  49;  galvanic 
current  through,  52. 

Fallacy,  of  electrodes,  113,  130. 
Fishes,  electrical,  75. 
Fleischl,  Von,  on  nerve,  130,  132. 
Frog's  tongue,  iii. 

Galvanisation  through  eyeball,  52. 
Galvanometer,  description  of,  151. 
Geranium  leaf,  109. 
Gotch    on    electrical    fishes,    75  ;    on 

malapterurus,  78,  81,  142. 
Gymnotus,  79,  80. 

Hering  on  colour-vision,  34 ;  on 
positive  polarisation,  73,  90. 

Berma7in,  polemic  with  du  Bois-Rey- 
mond,  14,  90,  121  ;  on  nerve-skin 
preparation,  61,  63  (fig.  29)  ;  on 
positive  polarisation,  73  ;  on  cat's 
skin,  97  ;  on  effects  of  atropin,  122. 


Hesitation,  period  of,  in  eye,  28,  33. 
Holmgren^  photoretinal   currents,    10, 

25. 
Homodrome  currents,  47. 
Human  skin,  86,  115,  116,  117,  119. 

Ivy-leaf,  electrical  response  in,  13, 

19- 
Ionic  velocities,  138. 
Ions,  importation  of,  125,  147. 

Kataphoresis,  133. 

Keyboard,  description  of,  155. 

Kilhne    and    Steiner    on     accidental 

current  in  retina,  27  ;  Kiihiie^  light 

on  retina,  54. 

Latency  in  eyeball,  28  ;  in  skin,  61 
(fig.  28),  99,  105. 

Lens  currents,  56. 

Life,  signs  of,  3  ;  latent,  5. 

Light,  action  of,  on  eyeball,  55. 

Lippmaftn's  capillary  electrometer, 
162. 

Living  matter,  properties  of,  3. 

Loeb,  osmotic  pressure  of  muscle,  134. 

Lost-time,  physical,  29 ;  in  oxidised 
copper  plate,  29  ;  in  cat's  nerve  ex- 
citation, 105. 

Luchsinger,  on  cat's  skin,  97,  122. 

MacDonald,  72,  140,  144. 

MacKendrick  and  Dewar  on  latency 
in  eyeball,  28. 

Malapterurus,  78,  79,  81. 

Malpighian  layer,  82,  83. 

Man,  skin  of,  119  (fig.  51). 

Matter,  properties  of  living,  3  ;  divisons 
of,  4  ;  currents  of,  85. 

Mercuric  chloride  on  skin,  65,  83. 

Mucous  membranes,  87. 

Muscle,  negative  of  variation,  4  ;  con- 
traction of,  8,  19  ;  modification  of, 
81;  (nerve-)  preparation,  92;  by 
A  C  B  plan,  94. 


INDEX 


175 


Negative  variation,  4,  16 ;  (abso- 
lutely), 76. 

Nerve-skin  preparation,  61  ;  response, 
100 ;  muscle  preparation,  92  ;  by 
ABC  method,  95. 

Newberry^  Percy,  on  seeds,  8. 

Oehle?-      on       action      of       mercuric 

chloride,  83. 
Orange  peel,  current  in,  86. 
Osmotic  pressure,  12,  134,  138. 

Pacmz's  law,  79. 
Permanganate  of  potash,  125. 
Photographic   record,    description    of, 

156  ;    of  current  in  retina,  26  (figs. 

10,  II). 
Physiology,  subject  of,  2. 
Plant  currents  by  A  B  C  plan,  94. 
Plant-guillotine,  13  (fig.  4). 
Polarisation  currents,  48  ;  positive,  y^, 

89  ;  in  electrodes,  130. 
Positive,  absolutely,  76  ;  polarisation, 

89- 
Properties  of  living  matter,  3. 
Protoplasm,  mechanical  excitability  of 

vegetable,  12,  84,  85. 

Quinke  currents,  133. 

Radium,  luminosity  of,  40. 

Raia,  79,  80. 

Reid,  on  eel's  skin,  66. 

Resistance,  119,  133,  142,  167. 

Resistance  of  eyeball,  45. 

Resistance  of  seaweed,  141. 

Resistivity  table,  168. 

Retina,  currents  of,  10  ;  action  of  light 

on,  10,  II,  37  ;  action  of  ansesthetics 

on,  38  ;  Engelmann  on,  39. 


Roeber  on  nerve-skin  preparations,  61. 

S-SHAPED  curve,  38. 

Sea- water,  168. 

Seaweeds,  141. 

Secreto-motor  nerves,  99. 

Seeds,  5,  6  ;  experiments  on,  8,  19. 

Shocks,  single,  on  eyeball,  45,  48. 

Signs  of  Life,  3. 

Skin  currents,  60  ;  by  A  B  C  plan,  94  ; 
normal  currents  of,  60  ;  (nerve)  pre- 
paration, 61  ;  Roeber,  Engelmann, 
and  Hermann  on,  61 ;  discharge,  82  ; 
human,  86,  116,  117  (figs.  49,  50), 
119. 

Solution-pressure,  18,  145,  146. 

Steiner  (and  Kiihne),  on  accidental 
current  of  retina,  27. 

Stomach,  frog's,  112. 

Strychnine  sulphate,  127. 

Subcutaneous  tissue,  86,  104. 

Subject  of  physiology,  2. 

Tarchajioff  on  skin  currents  of  human 

subject,  123. 
Tetanisation  of  eyeball,  42  ;  on  effect 

of  light,  44  (fig.  20). 
Tongue,  on  frog's,  iii. 
Torpedo,  78,  79,  80. 
Types  of  response  to  light  in  case  of 

retina,  29,  51. 

Vegetable  protoplasm,  mechanical 
excitability  of,  12  ;  surface,  109. 

Vine-shoot,  electrical  effects  of 
mechanical  excitation  (fig.  5),  15. 

ZiNCATiVE,  use  of  term,  14,  17,  104. 


PEIXTED   BY   OLIVER  AND   BOYD,    EDINBUEGH. 


_-QF341 

Waller 


WlSl 


